need advice

I’ve stared into a hole in the ice for the answer that never came so I thought I’d get your guys opinions.
Would you blow the parent whistle on teenage guys that are within the 9 month probationary 1 passenger limit but are hauling groups of thier friends around?
I hazed my 15 year old girls for riding with them but don’t know if I should go any further. After all, my girls and thier other girl friends made the decision to get in the car.
I don’t want to get these young guys in trouble but I don’t want to see anymore ‘little white crosses’ along the highways either. Especially if I could have done something to prevent it.
Instead of calling thier parents I’m thinking about sticking an unsigned note on the windshield of thier cars as a first and last warning prior to parental notice.
What do you think?
thanks