Most of the teens already know the warnings and pitfalls of smoking. To help your teen, you need to study the function of their behavior. What is the purpose of their smoking? Is it to be cool? Are they nervous or agitated? Are they doing it to fit in, all their friends smoke? Sit down with them and map out the purpose behind their smoking.
Once you have clearly defined the function of the smoking, then it will be much easier to define the circumstances needed to stop the smoking. I doubt that information about smoking and its negative effects will be an effective plan.
The plan must reflect the need to smoke. It may take a visit to a medical smoking cessation program, medication, nicotine alternatives, behavior modification, etc. Sometimes the purpose is oral gratification, this could be countered with electronic cigarettes, gum, or a bag of lollipops.