I need help with my son.?

im 17and my friends smoke pot and i use to... i doubt he was using the pipe for anything other than weed unless you have noticed a major change in his behavior... if you want him to stop, call his friends parents and say that you caught your son smoking and their kids might be doing it too... my friends dad did that to him and he was the biggest stoner out of all of us... he hasn't smoked pot since plus it got all our parents suspicious and so nobody ever wanted to do it at their house