You've already received some great advice, I'll just add my two cents. I've dealt with this on both sides of the issue. I've had neighbors who are nuisances, and I've had tenants who were nuisances too.
First of all, assume that they want to do what is right. Then as was mentioned, personally speak to the adults who live there. Not their 8-10 friends, just the tenants themselves. People are more reasonable when they are not surrounded by others that they want to impress. Also, you are showing that you respect them as possibly good neighbors. You may have to speak to them a few times before they make any changes.
If that doesn't work, then you can call the Citizens Service Bureau and they will report the problem to the appropriate organization while you will remain anonymous. If it takes a few calls to them, then so be it.
In the event that doesn't work, then you call the owners and let them know what is going on and that your next step is to call the police. No one likes police attention and that usually does the trick. Then if you have to, call the police. Who cares if they know you called, by this time they already know that you recognize them as a problem.