I had a similar issue when I lived in Garden Grove, CA. Had a dealer that lived right next door and we did not get along at all. The cross street at the end of my block was the dividing line between the 5th street and 17th street gangs, both Hispanic. Two blocks west was the line for a Vietnamese gang. I talked to my Hispanic neighbors that had kids and they agreed that the situation was bad but did not dare say anything out of fear. The police patrols in the area were pretty heavy and I spoke to them frequently. They said they could not do anything unless a crime reported and witnessed with proof of the crime. These bangers are not dumb and hide what they do pretty well.
I started out by confronting the "visitors" to the 'hood. They usually drive POS cars and they are basically rolling violations. Every time one drove too fast I got in his face and told them to slow down as there are kids on this street and if they kept it up I would tell the police. I made a point of writing down or taking a Polaroid of every car and visitor that stopped by. When ever a good neighbor saw me doing my business they would call the police and say that there was a crazy driver causing problems. The police would stop the offender within a block or two and issue citations, impound vehicles and sometimes make arrests for warrants. Eventually my neighbor threatened me. I immediately called the police and told them that my neighbor made a threat of violence and brandished a gun. They were there in less than a minute. They arrested him and he did 90 days. The other house guests moved out that evening. Never saw them again.
The downside was someone painted a gang drug house identifier on the curb in front of my house so I had some bangers knocking on my door in the middle of the night. I would call the police and provide a description of their car and pretty quickly they stopped coming around. For a "gang" this is a business and they would rather move to a new location than deal with legal hassles.
With parties and fights, as soon as the party gets loud and moves to the front yard, call the police. Enlist your neighbors to start calling as soon as it starts to get annoying. Eventually the police will get tired of your calls and do something about it, especially if the good guys in the neighborhood call too. Keep the pressure up on the bad guys and the police and the problem will go away. Ignore it and it will get worse. Don't give in to fear, exercise intelligent caution, call the police anytime it gets annoying.
It worked for me.