Telling him that he's going to die from lung cancer or trying to scare him out of smoking with the "black lung" routine probably won't affect the decisions he makes because he's young and thinks he's indestructible. Discussing how smoking can impair his athletic performance, his appeal to others (yellow teeth, bad breath, smelling like an ashtray), and his allowance (you can't continue to give him an allowance if the money could possibly be used for cigarettes) would appeal to him "where he lives."
Tell him that you'll research smoking-cessation programs for teens to get him some help. Start your search with the American Lung Association and your local Department of Public Health. It's also worth trying to appeal to his sense of being played for a sucker by tobacco companies, who attempt to lure young kids into becoming lifelong smokers. Try this mixture of empathy, support, and practical help. Remember, he's not trying to defy you by smoking; it's not easy to stop. Hang in there with him.