The victim, Deontae Smith, was shot to death at a block party attended by at least 150 people.
"I'm not accepting that no one knows anything. There were too many people. I don't want any one else's kid to be another Deontae," Tonya Burch said.
"We are never going to stop the violence in Chicago or this country until we make up our minds as citizens that we will not be quiet, we will no still, we will not be silent when evil goes on in our way," said Fr. Michael Pfleger.
After the billboard was unveiled, the group held an anti-violence march through the community.