Carol Reitner, 76, of Miami, said she heard about the vigil through an announcement at her church Sunday morning. "I was really devastated. It's really hard to believe that someone can take the life of someone else and walk out of court free," she said.
In Philadelphia, about 700 protesters marched from LOVE Park to the Liberty Bell, alternating between chanting Trayvon Martin's name and "No justice, no peace!"
"We hope this will begin a movement to end discrimination against young black men," said Johnathan Cooper, one of the protest's organizers. "And also to empower black people and get them involved in the system."
In Atlanta, a crowd of about 75 protesters chanted and carried signs near Centennial Olympic Park.
"I came out today because a great deal of injustice has been done and I'm very disappointed at our justice system; I'm just disappointed in America," Tabatha Holley, 19, of Atlanta said.
Civil rights leaders, including the Revs. Jesse Jackson and Al Sharpton, urged peace in the wake of the verdict. Jackson said the legal system "failed justice," but violence isn't the answer.
But not all the protesters heeded those calls immediately after the verdict.
In Oakland, Calif., during protests that began late Saturday night some angry demonstrators broke windows, burned U.S. flags and started street fires. Some marchers also vandalized a police squad car and used spray paint to scrawl anti-police graffiti on roads and Alameda County's Davidson courthouse.
In Los Angeles, police said a crowd of about 100 protesters surrounded an officer and eventually had to be dispersed by officers firing beanbag rounds.
Associated Press reporters Suzette Laboy in Miami, Terence Chea in San Francisco, Keith Collins in Philadelphia, Pete Yost and Eric Tucker in Washington and Luisa Leme contributed to this report.