Yamato Tanooka was left by the side of the road in woods in Nanae on Japan's Hokkaido island by his parents as punishment for throwing stones at passing cars and people. However, when they returned he was gone.
Despite a search by a now 200-strong rescue team, including members of Japan's Self-Defense Forces (SDF), there has been no sign of the boy.
"We still have no clue. We just do not know where he went," rescue team spokesman Satoshi Saito told CNN Wednesday.
"Our fatigue level is peaking now. But we will continue to search for the boy."
Weather hampers search
Thunderstorms brought an early end to the search on Tuesday, but clearer weather on Wednesday should allow rescuers to keep searching until nightfall, Saito said.
"We went through forest area roads towards the mountain yesterday and we will get deeper into the side of roads today," he said.
Hunters had joined the search on Tuesday after reports bear droppings were found in the area, but the information turned out to be false.
Saito said officials were considering the possibility that someone picked the boy up from the side of road but say he also could have wandered into thick mountain forests.
Lost in light clothing
Temperatures in the area dip below 10 degrees Celsius (50 degrees Fahrenheit) at night, compounding fears for the boy as he was only wearing light clothing.
Yamato was last seen in a black T-shirt, navy jersey trousers and red sneakers and did not have any food or a mobile phone.
He first went missing at around 5 p.m. local time (4 a.m. ET) Saturday, according to a spokesman for the Hokkaido Prefectural Police. Police got an emergency call about two hours later, the spokesman said.
Originally the boy's father told police his son had become lost during a family hike to gather wild vegetables, but later admitted he punished him for bad behavior.