If even one person is smoking weed inside a house, I can smell it from on the street. So if the 'entire teenage population' is outside getting stoned, the fuzz could probably smell it all the way back at the police station.

As a general rule, the best way to avoid police "interference" in parties is to obey the law. They tend to be pretty cool with you, if you're not causing any problems for anyone else, or busting out too many illicit substances.