hey kelina, i wish i could say something to actually help, but i cant just dont say anything, i'd like to show you some support at least.
maybe.. when you confiscated it, did you talk to him? have you talked to him about why is he doing that and how that makes you feel, how you are worried and how dangerous that is? i don't know how your relationship with him is, neither how he is usually, i'm 20 and i have had chances to use these things but i knew there could be no way out, specially because i've been alone (even living with my parents i was alone) and i always wondered why do people start doing those things in the first place... sometimes it's "for a try" and they can't get out, or they dont even know what they are doing you know?
i'd say to try to talk to your son and let him understand you, try your hardest to understand him too, be there for each other and if you can, get some help as madisgram said, both of you can get support and i really hope you two can talk and he accepts help. if his friends are into it with him, he needs to understand for himself and think for himself that its not good.