My pot smokin' stepson????????????

my stepson met theses new guys in school, and now he's smokin with them all the time, should I not allow the friendship?, he lives a few miles away, and now I have to drop him off and pick him up, so he can get stoned and have a good time with his friends, he's 16 years old. god knows I used at his age, but how can I help him do the right thing, ive been sober now for years, i miss a lot of the fun I used to have, but I'm much happier now, what should I do for him, or anything at all????????