"I just wanted to come and be here with everybody in solidarity and talk and pray and sing about where we go from here," she said.
At a youth service in Sanford, Fla., where the trial was held, teens wearing shirts displaying Martin's picture wiped away tears during a sermon at the St. Paul Missionary Baptist Church.
Hours after the verdict, demonstrators gathered on U Street in Washington, D.C., chanting, "No justice, no peace." One protester carried a sign that read, "Stop criminalizing black men."
In Florida, about 200 demonstrators marched through downtown Tallahassee carrying signs that said "Racism is Not Dead" and "Who's Next?"
In Chicago, black clergy members called for calm, with the Rev. Ira Acree of Greater St. John Bible Church saying the community should become "a united voice for peace" because it can't control the verdict but it "can control our streets and communities."
About 200 people turned out for a rally and march in downtown Chicago, saying the verdict was symbolic of lingering racism in the United States.
Seventy-three-year-old Maya Miller said the case reminded her of the 1955 slaying of Emmitt Till, a 14-year-old from Chicago who was murdered by a group of white men while visiting Mississippi. Till's killing galvanized the civil rights movement.
Miller said she felt as if "nothing has changed in 58 years."
The NAACP called for the opening of a civil rights case against Zimmerman in an online petition addressed to Attorney General Eric Holder.
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.
In Oakland, Calif., 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 two people threw bottles when more police arrived. The officers used beanbag rounds to disperse the crowd.