I hate to say it, but other than present the facts of the dangers, and punish when you do smell it on his breath - in other words, when you catch him, HE's got to be the decision maker.
He has to know how girls (and others) look down on smokers. Even coworkers look down on them, as will any prospective employers or those he interviews with for college. Cigarette smell is easily detected. Even moms of young kids may stay away, as it's been found that the residue on clothes even gets into lungs.
I smoked occasionally as a teen. I was surprised at how easily my parents stopped punishing me for it, when they would be too harsh on so many other things, or even perceived faults. I was grounded at the blink of an eye, often for things I didn't do. To me, that gave me a sign that although they preferred I didn't smoke, it wasn't bad. This is a life-threatening thing. I think punishment is needed. He will still sneak, probably, but this isn't anything I'd waver on. In my twenties I became a social smoker - never craved it, never smoked alone. Today I don't smoke at all. I never became hooked, but as we know from others, it is easy to become hooked.
I'm sure he's hanging with the "wrong" crowd - those that do smoke, and it's a very social habit. But I don't think you'll be able to change his friends. Smoking isn't cool, and he needs to know the smell follows him everywhere. I have to hold my nose and often my stomach when I pass a smoker. Ick!