"As a white person I hate to see this and to say, you know that make a generalization that racism is still strong," protester Billy Dodd said.
Civil rights activist the Rev. Jesse Jackson said people need to keep the pressure on for justice.
"They'll be civil law suit filed that we should rally around," Jackson said. "We can all urge the Department of Justice to rally around and they must."
The Justice Department said it is looking into the case to determine whether federal prosecutors should file criminal civil rights charges now that Zimmerman has been acquitted in the state case.
In Miami, more than 200 people gathered for a vigil. "You can't justify murder," one poster said.
Another read, "Don't worry about more riots. Worry about more Zimmermans."
ABC News' Betsy Klein, ABC News Radio and The Associated Press contributed to this report.