Homeless/abandoned teen help?

There is a kid in my neighborhood that is homeless,and has no parents with him. He goes to his friends house and stays for prolonged periods of time until he is forced to leave after begging to stay. He was ones kicked out of my friend's house and now has a restraining order to not go in it even if he is invited. Then he lived at another friend of mine but this time my friends parents agreed for a certain amount of time. Now he is just staying at ANOTHER friend's house for who knows how long. I can't talk my friend into kicking him out, he keeps saying it would be a horrible thing to do but the homeless child (by child I mean 16yrs) has no parents (his mom pretty much abandoned him) his mom sends him 50$ each week for food but he just blows out his money on drugs, and is just an overall bad influence to everyone. I want to help both my friend and the homeless kid but I dont know what to do. Should I contact the local sheriffs office? I know this is a pretty hard story to believe but it's 100% true. I don't know if it's legal to let a minor live in your house with out consent from a guardian and no rent either.What should I do? I would feel very irresponsible if I didn't do anything because something could happen to one of them and I would feel like I could have prevented it.