Reading this, is like a flashback to a couple of weeks ago for me and my husband. One of his close friends passed away last fall, leaving behind his wife, and a 22 year old son. Well the son fell apart after his dad died, and has been in all kinds of trouble. He dropped two semesters of college, has been using cocaine, drinking too much. Had major problems with his mother, and she finally got to the point where she bagged up his things and left them on the porch telling him to go. But when he came knocking and yelling and banging on the door demanding entry back in; she called my husband.
We now have "the kid" as I call him here, living with us. Same worries as you are having, if he is out there on his own, he will be living with his drug friends, maybe get deeper in addiction and drinking.... My husband got it in his head he can help him, and so that is where we are at now.
I dont have advice for you. I dont know if we are doing the right thing. Right now it is going ok actually but who knows what the outcome will be. Our thread is called "Housing a young Coke addict" if you want to read it.
I guess just wanted to say, your not alone.