Los Angeles (CNN) -- Dismayed, angry but saying they'll fight in a new struggle for civil rights, protesters marched peacefully Tuesday in Houston, Atlanta and Florida while thousands of Americans found other ways to demonstrate their feelings.
Pro boxer Terrell Gausha told the entertainment news site TMZ that he would no longer wear the American flag. News filtered out that entertainer Stevie Wonder said he will no longer perform in Florida so long as the state's controversial Stand Your Ground self-defense law remains in effect.
A mocked-up image of Martin Luther King Jr. wearing a hoodie went viral on the Internet. And a page on the popular blogging service Tumblr drew hundreds of often poignant essays from people -- many of them white, middle-class and far removed from the civil rights struggle -- who said the death of 17-year-old Trayvon Martin, and Zimmerman's acquittal, had moved them profoundly.
"I think if I looked like Trayvon I could've been shot or arrested or antagonized and hated. I could've been dead at 17," wrote one poster who identified himself as a 31-year-old white man. "I think if Trayvon looked like me he could've grown up to be someone that did something wonderful for the world."
A Florida jury acquitted Zimmerman Saturday following a nearly four-week trial. The Hispanic former neighborhood watch volunteer acknowledged shooting and killing Martin last year, but said he did so in self-defense after the teenager attacked him.
Critics of the verdict, however, say they believe the jury got it wrong -- that Zimmerman was an overzealous wannabe police officer who racially profiled Martin and hatefully shot him down. They want federal civil rights charges and changes to laws like Florida's Stand Your Ground, fearing a spate of similar incidents.
"Anyone walking or committing no crime can be followed or approached by another civilian and they can use deadly force and say it was self-defense," the Rev. Al Sharpton said Tuesday in Washington. "That is something that is frightening and cannot be allowed to sustain itself in our society."
Although Zimmerman's attorneys did not seek a Stand Your Ground hearing before trial, the judge's instructions to the jury did allude to provisions of the law, and a juror interviewed by CNN's Anderson Cooper on Monday said it came into play during deliberations.
Call for change
Sharpton's National Action Network is planning 100 protests across the country Saturday calling for civil rights charges against Zimmerman.
Similar calls echoed across the Internet. As of Tuesday afternoon, more than 490,000 people had signed a MoveOn.org petition started by the NAACP asking for the Justice Department to file civil rights charges against Zimmerman.
Two petitions to the White House seeking such charges had more than 30,000 signatures between them Tuesday morning. Petitions in support of Zimmerman had a few thousand signatures.
Since the Saturday verdict, protests have occurred across the country, including New York, Washington, Boston, Atlanta, Houston, Las Vegas and Kansas City.
"I was devastated, a little bit heartbroken. But this is as much as we can do," protester Kennan Blair told CNN affiliate WSB during Monday night's protest there.
In Cleveland, protesters gathered on the steps of the Cuyahoga County Justice Center carrying bags of Skittles -- the candy Martin had just bought before he was killed, CNN affiliate WEWS reported.
"I could have been Trayvon Martin," one African-American teen wearing a hoodie -- the same garment Martin was wearing -- told the station. "But this case isn't about racial issues. This case is about violence. This case is about the judicial system."
-- Protesters in Florida staged a sit-in Tuesday at the governor's office, demanding a special legislative session to consider changes to the Stand Your Ground law, a spokeswoman told CNN.
-- In Houston, police on horseback and bicycles shepherded protesters staging a protest outside the Harris County Courthouse.
-- In Atlanta, civil rights leaders gathered to denounce the verdict and announce their participation in Sharpton's planned rallies Saturday. "Our message to the public is clear," the Rev. Markel Hutchins said. "This is not over, all is not lost. There is still hope and we must continue to fight."
Some protests have turned violent.
In Los Angeles, police went on emergency footing for the third night in a row Monday after violent demonstrations wracked part of the city, CNN affiliate KCAL reported.They warned over stricter enforcement beginning Tuesady.
In Oakland, demonstrators threw rocks, bottles and firecrackers at police, Officer Johnna Watson said early Tuesday. Authorities arrested nine people there, she said.
Appeals for calm
Civil rights leaders appealed for calm out of respect for Martin and his family.
"His name and memory should not be smeared by reckless violence," Sharpton said.
Civil rights leader, John Mack, now a member of the Los Angeles police commission, said those behind the violence "have their own agendas that have nothing to do with justice, and very little to do with Trayvon Martin."
Taking Zimmerman's side
Of course, not everyone disagreed with the jury's verdict. On a Facebook page dedicated to discussion of the trial, Facebook user Lorraine Keeley said the jury got it right.
"The jurors have spoken. ... kudo's to this great defense team," Keeley wrote.
More controversially, conservative rock singer Ted Nugent called Martin a "dope smoking, racist gangsta wannabe" in defending the verdict in a column for the website Rare.
"Here's the lesson from all this, America," Nugent wrote. "Teach your children to not attack people for no good reason whatsoever. Conduct yourself in a responsible, civil manner, and everything will be just fine. Try to kill someone and that someone just may be exercising his or her Second Amendment rights and you could get shot. It's called self-defense, and it is the oldest, strongest and most righteous instinct and God-given right known to man."
Meanwhile, Zimmerman's parents, Robert and Gladys Zimmerman, offered more conciliatory words in an ABC interview.
"We are deeply sorry for this tragedy," Gladys Zimmerman said.
CNN's Michael Pearson and Holly Han reported and wrote from Atlanta; Cheri Mossburg reported from Los Angeles; CNN's Tina Burnside, Dottie Evans and Dave Alsup also contributed to this report.