In a matter of minutes, they left a trail of broken glass and doors.
It happened on Rosemar Court in the hills above the Alum Rock neighborhood.
ABC7 News learned people found out about this vacant-home party on social media and ended up leaving nearly $50,000 worth of damage.
Muddy footprints left on doors show how the vandals broke in through the garages, so they could get inside.
All six new houses had their first public showing Saturday and that night, it's believed a group decided to use them as a party site. Street lights were broken to give them cover.
Heather La France is a listing agent on one of the houses and is familiar with these so-called "break-in parties." "It becomes sort of a thing where they send a viral invitation out and I heard that it might be a disappearing invitation, some sort of Snapchat link, and all of a sudden kids from everywhere come and have a party," she said.
The house at the end of the court sustained the most damage as the front windows were smashed and the stucco was damaged. In addition to that, the glass fireplace screen was broken. And in the kitchen, the stainless steel refrigerator door was gouged; two cabinet doors were ripped out and a second-floor railing had slats kicked out.
Construction crews were disappointed to see six months of work vandalized. Now, they're working on repairing the damage. "We took all our energy to build these houses and just to hear out of nowhere in 10 minutes, they did a lot of damage. Yeah, it hurts a lot because I mean, we built them from the ground up," construction worker Jose Garcia said.
A 20-year resident of the neighborhood said this happened before at a vacant house up the hill. "You hear them up there making noise. I called the police, sometimes they'd come, sometimes they wouldn't come. And when they came, they had already left, so it was too late," San Jose resident Al Garcia said.
San Jose police said they're not familiar with these "break-in parties."