My friend is seriously Schauspielen up

He's lying to ppl, he's messing around with ppl's feelings and he punched a freaking window. None of his other Friends wants to help me hav an intervention and i'm scared if i do it on my own he wont listen and he'll just start treating me lyk he is all his other friends, plus i hav no idea as what to say to help him cope. Any helpful advice????