There's a long list of things I would do, ignore it if it's not for you:
"I will only buy you things from now on, you will get no money because I won't risk my child being arrested for criminal activity - you might not know how it will affect your future but I do"
Buy nothing he can sell - write his name on things in marker pen (Xbox for example)
Get the police in to talk to him
Don't cover for him - call the police if you find drugs - search his room, he's not entitled to privacy if you as the adult can get arrested for having drugs in your home
Not allowed out without a clear activity in mind - take him, pick him up - if he gets out, find him (if he's in the park with drugs and mates, call the police who will turn up and search them)
Try to get other parents on side and involve them
Zero tolerance to illegal activity - it's easier if you just pick the law and get him to comply, no wiffling about whether you don't think cigarettes are as bad, or weed isn't as bad - just pick the law and have zero tolerance - if there's cigarettes, rizla papers, drug paraphernalia throw it out at home - he's under 16 he can't smoke or drink
Change the house language - if you were previously liberal because you wanted to encourage independent thinking etc and you think that's made him in any way think he can bring trouble to your door then stop it. I just keep saying ' in this house we comply with the law no matter whether we privately think differently'
More family time, parenting at this age is not easier because you're trying to encourage responsibility - get him into touch but safe stuff if he's a risk taker - BASE jumping, rifle shooting, bungee jumping, hard activities that are physically tiring but also exhilarating where he feels he can develop self esteem and self worth - it's especially hard parenting a risk taker, you need eyes in the back of your head and you need to be on top of your game
Don't trust him. Be more clever. Stalk, follow, manipulate. You're trying to keep him alive, safe, free of a criminal record. Be smarter than him, pretend you're not by all means to get information.
Lock down your internet parental controls. No adult websites doesn't just mean no porn, it means no druggy websites. No 3 or 4g on his phone. Cancel contract, control wifi.
Keep him very busy. Spend your money on risky but safe controllable activities.
As I said, ignore anything that's no good to you  - my perspective is skewed by the circumstances I've been in fostering teenagers who have heavy police/social work involvemen
Anything but this above. Sure fire ways to push him away and more into the scene. Not one of them will discourage him other than more family time. In fact, possibly the worst post I've seen.