Sorry but this is the most hillarious thing I've read all day
Too many people here have chosen to find your neighbour guilty until proven innocent.
If these are young people then chances are they have a lot of active friends who've all got cars? Do you have enough spare time on your hands to document every different person that goes in and out of the house?
Living up to the student stereotype I've bought from a fair amount of different people, all of which have been pretty decent people that don't cause trouble or sell crack/coke/heroine or start pimping businesses! (I'm laughing here again). You're terribley misguided.
Vini, If they're not causing you or your area any trouble then there's no need to cause them any trouble for the sake of it. If you have a good reason to believe they are, then by all means report it.