How do you get victims to come forward?

I found an article about a person i once unfortunately knew getting arrested for theft and burglary. The comments on it confirmed what i suspected about him having multiple victims. I was able to get one to talk to me with fake gmail accounts we both created but the others were too scared and this one was too scared and not ready to go to authorities. This guy is incarcerated right now but he wont be forever. He's preys on single mothers and their children. He also worked at a homeless shelter for families and was asking for diapers and baby wipes over facebook he said he would take to hurricane victims with children. He will probably be worse when he gets out. How do you stop a person like this? How do you find victims who might feel safer if there was more of them coming forward? He's very violent too. Everyone is terrified of him.