Honestly, by the time I have adolescent kids, I plan on having a fully operational medical marijuana grow farm operation, so if they are found without baggies of bud around them I'd be even more suspect.
But really, it would take a lot for me to call the cops on my kid, and a QP baggied into dimes is hardly a huge sin in my eyes. The assault and running away would be the fear factor, and like I said, if they didn't return within 24 hours I'd then get the police involved, just because that would be the point where he safety really is in jeopardy. Unless he's getting his stuff from some nasty black crack dealer on the street corner in the ghetto, which I'm sure he's probably not. With my experience, aside from young boys, older, middle-aged women are the most common dealers I've come across. He probably has a buddy at school whose mom hooks him up, or something along those lines. Dealing pot on a small scale in safe area to people you know isn't really as dangerous as most people who've never bought or done drugs can really understand. It's not likely a 16 year old is gonna be in a position where he owes a whole bunch of money to some gun-wielding gangsters. The biggest problem here, obviously, is the broken laws and getting the cops involved, but if it came down to it, for a hormonal, stoned 16 year old boy it might be necessary.