This is a tough one. I am going through about the same thing.
Briefly, I discovered my teenaged son was smoking the small cigars, and a little while later, cigarettes. I hit the roof and wanted to strangle him. After I cooled down a bit, I confronted him, reminded him how he hounded me to stop smoking all during his youth, how he watched me struggle trying to quit, and what a horrible waste of health and money a smoking habit is. I tried the "logic and reasoning" approach.
I also reminded him that there will be other serious consequences (from yours truly) if he did not stop with the tobacco.
I set him up with an ego battery and some 0-to-6mg nic juice, telling him that if he absolutely feels the need to have tobacco, use the 0-nic, as he has witnessed me vaping over the last year. I am relentless (but not overly so) in staying on top of this, and regularly ask him how he is doing with the vaping or smoking. I believe I have made some headway, as he tends to offer up information now, as in, " I didn't feel like having anything at all today, Dad", for example. The funny thing is, that I am almost certain that he does not vape or smoke during the day because he is in school all day, and has sports afterward all year long.
Most kids will try some things and experiment. I hope I caught this in time, as I am not in favor at all of encouraging smoking OR vaping for the young. If I have to choose though, it is vaping 0-nic all the way.
Good luck with this. This can be a particularly troubling situation, as I am completely aware. (And I still want to strangle him..........)