Can my friends get in trouble if I was pulled over and I wasn't drinking but my friends are drunk?

I have a simple question. I occasionally drink but not much, and when I do, I don't drive, but when I'm with friends at their house and they drink, I'm usually the one to drive. Now, my main concern is, what trouble can everybody in the car get in to. I have read, that if there is no alcohol in the vehicle, the drive (me in this case) will not get in trouble if I have not drank anything, and if I didn't supply the alcohol, which I cannot since I'm not 21. Now, I want to know if my friends can get into trouble if I were to get pulled over for something as stupid as a 'dim' license plate light. If they CAN get into trouble, what would happen to them? I understand some cops are more strict than others, and I haven't read the whole Zero Tolerance rule, but my impression, is the Zero Tolerance Rule applies if they drive. Am I correct, or does it apply even if say, he was walking down the road? Also, this is another question, but its directed into what I should do. My friend likes to drive, even after having 5 (strong) beers. He does it all the time, and I think he is the most idiotic person I know for doing that. Anyway, I want an opinion. If you were in my position, would you even consider ratting them out? I've thought about calling and reporting a drunk driving, as he goes home, but never have, JUST because he needs to learn that he isn't going to get away with it.