I caught him smoking, in his room 
. I went nuts (as you would) he started crying and when we we both calmed down we had a talk about why he was doing it.
It turns out he has been smoking for a while and a lot of his mates smoke, Ive put consequences in, grounding, given him a lecture about how dangerous it is
He was very honest with me and said he feels anxious and stressed a lot (he has asd and adhd) and his relationship with his dad has hit an all time low and he is very upset about that. He has problems at school which are not helped by the schools attitude and lack of support and ds says smoking helps calm him down 
I can't be angry with him, I just can't. I'm disapointed and upset that he has started to smoke but he has been through so much. He has struggled to accept his diagnosis of asd and its either his way or the highway.
All I can do is put in boundaries around the smoking, he never ever does it in front of me or the other dc, I will not be providing him with money to smoke and just hope he sees the light.
So come on I'm a fool aren't I? But Ive been through so much with ds, violence, aggression, truanting, asd diagnosis and so on that I just can't get worked up about the smoking (although it worries me yes) and he's only 13.