There's an empty lot near our building and it gets occupied by students a lot. I just open my window and shout (I am the "Ruhe bitte guy"). From their perspective, someone is crazy enough to shout outside the window, so it works 100%. My next step would be calling the police but honestly never had to do this. Even if I did, the police in Germany are usually too kind to scare them :)

I don't feel like any sane person can reason with drunk people (worse, teenagers) who are making noise at 2 am - except when they are your neighbors or you know them somehow.