Don't take me wrong, I do not know neither one of you (father and son), but if I were a parent I would never, ever, allow a son of mine to smoke, specially if he was underage. But, ignoring that part, I would do my best to keep him away from cigarettes. I wouldn't buy him an e-cig, we all know how yummi and addictive it is. At least, I always have mine near me.
What I would do is, take him out of cigarettes and give him an old setup of yours. If you have some old ego batteries put a clearomizer or something similar and toss the worst flavor you have! It will be similar to "shock" therapy. He will have the nicotine "fix" and he won't enjoy it at all. At that point you will have to be strict, you can't allow him to have any analogs otherwise he will just stick with those. I would also say, avoid vaping in front of him. There's no need to make him "suffer" making him vape terrible flavors and see you vaping on the good ones.
Remember, you are that father, you are the man. Be strict and make the rules. If you see him or hear stories about him smoking take is computer for a week, that will show him. He his too young to have his life destroyed by cigarettes.