When my daughter was still a minor and I knew she was doing drugs, our money supply went out the window. She did get a job, which actually was a good thing, and that was her only money. It kept her off the street a few nights a week. I'm sure she didn't use that money to the good all the time, but at least it didn't come from us. We also made her pay for her own "toys" except for essentials such as food and minimum clothing (Walmart and just enough). We bought it for her. Money never went into her hands from us once we realized she may take it a nd use it to buy drugs rather than for the reason it had been given her. The car was not something we let her use after she got into one accident. We hid the keys. She stomped around a lot telling us how mean we were, but as long as she was using drugs, we were not going to reward her and we didn't trust her on the road. And we didn't trust who she'd pick up and drive around in our vehicle either. We tried to get her help, but she wouldn't cooperate. She ended up having to leave after she turned eighteen because she would not follow our rules and our younger kids did not need to see her tantrums or the police coming to the house looking for her.
I would take away all of his methods of contacting his "friends." Does he have his own cell phone and computer that you pay for? It may not stop the drug addiction, but at least it shows your disapproval and that t here are serious consequences and denial of fun if he chooses to self-destruct. I don't know how close he is to eighteen, but you may have to consider detachment once he turns eighteen. That can mean asking your child to either follow your rules and also go to rehab and take it seriously...or leave the warmth of your home....
I hope things get better. Keep posting.