i went through a phase like that not too long ago. around the age of 16 aswell. now that i think about it it is very worrying how easy it is to get hold of such things. i think it would be a great idea to talk to your son about it. my parents didnt talk to me about it. all they really did was shout at me and ban it. which made things worse. but after a little bit i just wasnt bothered with it anymore which happens to a lot of people.
im not too sure it would be a good idea to talk to your sons friend as this could get you on bad terms with his parents. but as to talking to your son please do. my phase would have stopped earlier if my parents had sat me down and talked to me in an adult manner about it.
i hope everything goes well for you and your son realises he doesnt need these things to enjoy life to the full.
good luck with everything,
eoghan