The Justice Department launched an investigation of the Martin killing three weeks ago.
"I know that many of you are greatly and rightly concerned about the recent shooting death of 17-year-old Trayvon Martin, a young man whose future has been lost to the ages," Holder told the 14th annual convention of the National Action Network, three days of discussion on race issues.
"If we find evidence of a potential federal criminal civil rights crime, we will take appropriate action," said the attorney general. "I also can make you another promise: that at every level of today's Justice Department preventing and combating youth violence and victimization is, and will continue to be, a top priority."
Holder was interrupted at least half a dozen times by the audience during his speech with affirmations of "that's right" and "there you go," including when he said his department was working with the Department of Education, state, local, and community leaders and stakeholders to get rid of the school-to-prison pipeline.
His comments followed word Tuesday in Florida by the special prosecutor in the case that she would soon make an announcement. She has not given any more details.
Martin's parents were to speak later at a news conference at the meeting. Also Wednesday, New York City Mayor Michael Bloomberg and leaders of African American organizations planned to announce in Washington a national campaign against "stand your ground" self-defense laws.
At an earlier news conference in New York, Bloomberg said state and local lawmakers who had previously supported laws similar to Florida's were having second thoughts.
"You just cannot have a civilized society where everybody can have a gun and make their own decisions as to whether someone is threatening or not," Bloomberg said. He said America, "where there are more guns than people," is the only democracy with such laws.
The attorney general says that Justice Department officials including Tom Perez, the assistant attorney general for the civil rights division, and U.S. Attorney Robert O'Neill from Florida have traveled to Sanford to meet with the Martin family, members of the community and local authorities.
He says representatives from the department's Community Relations Service are meeting with civil rights leaders, law enforcement officers and residents to address community tensions.
Neighborhood watch volunteer George Zimmerman says he shot Martin in self-defense after following the teenager in a Sanford, Fla. a gated community outside Orlando on Feb. 26. He said he was returning to his truck when Martin attacked him and that he shot the unarmed teen during the fight. He wasn't arrested partly because of Florida's "stand your ground" self-defense law.
The lack of an arrest has led to protests across the nation and spurred a debate about race and the laws of self-defense. Zimmerman's father is white and his mother is Hispanic. Martin was black.
On Tuesday, Zimmerman's attorneys announced they were no longer representing him and that they had not heard from him since Sunday, although he had contacted talk show host Sean Hannity and the special prosecutor.
Martin's shooting served as a theme for the three-day gathering of National Action Network activists. Charles Ogletree, a Harvard law professor, said at a panel following Holder's speech that Trayvon Martin is "a symbol of what's wrong" with the criminal justice system.
"I want to see the first black man who uses the 'stand your ground' defense and see if it works. Or the first white victim of the 'stand your ground' by a black defendant and see if it works," Ogletree said.
Laura Murphy, director of the Washington office of the American Civil Liberties Union, said she lived in a development that transformed from mostly black to mostly white. She said she sent emails to her neighbors when her son was home from boarding school that pleaded, "Please, do not call the police, because if you see a young black man walking around the neighborhood with a hoodie, that's my son."
She urged the audience to pack a Senate subcommittee hearing next week on proposed legislation that would ban racial profiling in law enforcement, among other things.