"It was a year of horror, of waiting, but it feels like yesterday," he told CNN ahead of the anniversary.
The disaster and its aftermath -- when armed men initially prevented international monitors from reaching the crash site and recovering the scattered bodies -- shocked the world.
As the months have passed, almost all the victims' relatives have had the bodies of their loved ones returned to them for burial.
But the body of Piet's brother Alex Ploeg is one of only two of which no trace has been found.
Piet Ploeg told CNN how the family struggled to come to terms with the uncertainty of having no remains to lay to rest.
"I cannot understand very well how it is possible that just two people are vanished ... blown away," he said. "It's beyond belief, I can't understand it."
The bodies of Alex Ploeg's wife, Edith Ploeg-Cuijpers, and 21-year-old son, Robert, were recovered and the family held a funeral for them in November. They also remembered Alex, who was 58, at the ceremony but had only a picture to display.
"You want to believe that your brother will come home. He didn't come home," Piet Ploeg said.
Several Western nations and the Ukrainian government have accused pro-Russian separatists operating in the region of shooting down the plane with a missile. Rebel leaders and the Russian government have repeatedly disputed those allegations.
Piet Ploeg is pointing no fingers. He just wants the right party to be held responsible.
"It could be Russia
, it could be Ukraine
, it could be the separatists. I think it is important that they find out who did it, who was responsible for it," he said. "I'm not very interested in who pushed the button, but who was responsible, which organization, which country."
How is the anniversary being marked?
Commemorative events were taking place Friday in the Netherlands, Ukraine and Australia.
The greatest loss was suffered by the Netherlands, which had 196 of its citizens on board the flight, which took off from Amsterdam bound for Kuala Lumpur, Malaysia.
But dozens of Malaysians and Australians were also on the plane, as were smaller numbers of UK, Indonesian, Belgian, German, Philippine and Canadian nationals.
Ukrainian President Petro Poroshenko paid respects to the victims and their relatives in a video message Friday. "Today, our people recall this tragedy and share the grief and sorrow of the families who lost their loved ones," he said.
Ukrainians laid flowers outside the Dutch Embassy in Kiev, and a ceremony is also planned at the crash site.
What do we know about what happened?
The Dutch Safety Board
is leading an international investigation into the crash, at the request of Ukraine, which remains locked in conflict with pro-Russian separatists in its eastern Donetsk and Luhansk regions.
The Dutch accident investigators have not yet released their final report, but the evidence points to the separatists
as being responsible for shooting down MH17, according to a source who has seen a draft investigative report.
The final report is expected to be competed and published in the first half of October.
In its preliminary report on the disaster
, the Dutch agency said Flight 17 broke apart in the air after a burst of "high-energy objects" hit it from outside, supporting the theory that a warhead exploded close to the jet.
Piecing together what happened has not been easy.
The vast crash site was left unsecured after the disaster, and international investigators struggled to reach the area amid fighting between the separatists and Ukrainian government forces.
The rebels were widely accused of looting the site, tampering with evidence and stopping investigators from combing through the wreckage.
Only in November could experts start to recover the mangled debris of the downed airliner from the Donetsk farmland where it came to rest.
Will anyone be prosecuted?
The lead prosecutor in a separate criminal investigation into who brought down the plane said that investigators had identified "several" persons of interest but that it was too early to say they had identified suspects.
Investigators have been denied access to certain information in Luhansk, including records of cell phone calls, Fred Westerbeke told CNN, but they did get access in Donetsk.
Investigators are looking at different scenarios, he said, but "most of the information we have points to the use of a Buk rocket being fired from the eastern part of Ukraine."
It's been a difficult investigation to pursue, Westerbeke said. Nonetheless, he's optimistic the case will one day be brought to court.
"I really believe we will have a prosecution, yes," he said.
"Will the suspect be arrested and handed over for prosecution? That is more difficult to answer."
The criminal investigation may be completed by the end of the year.
What happens next?
Australia, Belgium, Malaysia, the Netherlands and Ukraine have called for the United Nations Security Council
to set up an international criminal tribunal to try those responsible for bringing down the plane.
"Justice for the victims from the first moment has been our top priority," Dutch Prime Minister Mark Rutte said this month. "We are now asking support in the United Nations for the creation of an international tribunal."
But Russia has pushed back against the idea.
In a call with Rutte on Thursday, Russian President Vladimir Putin
said Russia wanted a thorough investigation, but he criticized "premature and counterproductive initiatives from several countries, including the Netherlands, to establish an international tribunal," according to a Kremlin readout of the call.
Speaking to reporters the same day, Russian Foreign Minister Sergey Lavrov suggested that the United States wanted the tribunal so it could punish those it already believes to be responsible. The U.N. Security Council has nothing to do with the MH17 investigation, and the creation of an international tribunal would be unprecedented, he said.
So who is to blame for shooting down the plane?
That remains a hotly contested question.
The draft Dutch investigative report said the evidence indicates that a Buk -- a Russian surface-to-air missile -- was used, launched from a village in rebel-controlled territory, according to the source who's seen the document.
But Russia denies any involvement. And its officials have repeatedly pointed the finger instead at Ukraine, suggesting that a Ukrainian fighter jet shot the plane down, or that Ukrainian ground forces were responsible.
Earlier this week, state news agency Tass quoted Russian Investigation Committee spokesman Vladimir Markin as saying it is inclined to believe the plane "was hit by an air-to-air missile
," rather than a surface-to-air weapon, and that "the missile is not Russian-made."
A day later, Tass cited the deputy head of Russia's aviation agency, Rosaviation, as saying one possibility was that the plane was shot down by a 9M38M1 surface-to-air missile fired from the Buk-M1 air defense system -- a missile discontinued by Russia since 1999.
The official, Oleg Storchevoy, was citing a report by Russian air defense system manufacturer Almaz-Antey in June, which also pointed out that Ukraine had received many of the type of missiles in question. However, analysis of that report by IHS Jane's Defence Weekly
said that even if the missile type was proved, the question of who fired the weapon was unresolved, and that the pro-Russian separatists certainly had more reason to do so than the Ukrainians.
Heather Conley of the Center for Strategic and International Studies told CNN there was "so much overwhelming evidence," and while the Kremlin can continue to deny any Russian involvement, "it just does not stand (up) to any test."
What do the pro-Russian separatists say?
In the days after the crash, Alexander Borodai, then the self-declared rebel Prime Minister in Donetsk, told CNN he believed Ukrainian forces either shot the plane down with a surface-to-air missile or one of its own fighter jets.
"We didn't have motives and desire to do that, and it is obvious that Ukrainians have them," he said. "I can't say about desire, but motive is obvious that the crash of this plane was beneficial to them."
What is the current situation in Ukraine?
A shaky ceasefire was agreed to in February, but the bloodshed has continued -- though on a lesser scale -- as the pro-Russian separatists and Ukrainian forces battle for control of the Donetsk and Luhansk regions.
The number of ceasefire violations has been increasing lately, climbing to more than 100 a day, according to the Joint Ceasefire Coordination Center, set up last year by Ukraine and Russia.
About 80% of ceasefire violations are taking place around the city of Donetsk, which is held by the separatists' self-proclaimed Donetsk People's Republic. Fighting around the shattered Donetsk International Airport continues around the clock, the center said.
This week, eight Ukrainian soldiers were killed and 16 injured in 24 hours, Ukraine's National Defense and Security Council told CNN, some as they checked anti-mine equipment in Luhansk, near the Russian border.
Is there any resolution in sight?
Not so far. Western leaders have called on all sides to implement fully the terms of the truce signed by Ukraine, Russia, pro-Russian separatists, France and Germany in Minsk, Belarus, in February.
They have continued to put pressure on Moscow, which they accuse of backing the separatists with equipment, training and Russian troops -- through a range of financial sanctions imposed against Russian interests.
Those sanctions were extended last month, prompting Kremlin spokesman Dmitry Peskov to say Russia would respond by extending measures against the European Union, which include restrictions on the import to Russia of EU foodstuffs.
NATO Secretary-General Jens Stoltenberg warned last month that while Europe faces many crises, "none is as complex as the crisis in Ukraine." He also called on Russia to "stop its aggressive actions in Ukraine."
There's little sign of diplomatic progress, though. While Moscow denies any direct involvement in Ukraine, Putin has accused NATO of raising tensions by advancing toward Russia's borders.
How did we get here?
The unrest began in late 2013, leading up to the Ukrainian parliament's ouster of pro-Moscow President Viktor Yanukovych in February 2014. Russia annexed Ukraine's Crimean Peninsula a few weeks later, with fighting breaking out that April in two Ukrainian regions bordering Russia -- Donetsk and Luhansk.
Separatist leaders there declared independence from Ukraine
and sided with Russia. Despite the efforts to forge a peace deal, there's been no letup in the violence. Many people in eastern Ukraine speak Russian and look to Moscow, not Kiev, for direction.