Well, if what you said was true. Thats a stupid reason to do drugs just because of the clique he hangs out in.
Starting out with cocaine is probably one of the worst things he can do. At 15, 16, cocaine can easily kill you. It speeds up your heart so much. A tthat age you can't handle it.
Especially if he's doing cocaine, he's probably going to drink in excess. This will kill you even faster. The coke will speed you up, and the alcohol will slow you down. Your heart will stop.
Its just not good. Cocaine is easy to abuse. Plus, its auto-jail if you are caught with any. NO exceptions.
If he doesn't listen, atleast try to sway him to something easier. Like pot. Usuually one hit of pot most people will be done with drugs.
Actually if you want, show him
http://www.i-doser.com/. Its waves that produce the same effect as some drugs. Then tell him to look it up on Limewire. Tell him to rey coke on that before trying it irl. I'm pretty sure he won't want to do the real stuff.