Police were initially brought in shortly before 11:30 p.m. to Jefferson and Sydenham streets where an estimated 600 to 800 young people were gathered.
"Kids acting like kids, but wild kids. They were kids acting like adults pretty much," said Trey Brown who passed through the large crowd on his way home.
The window of one of the first arriving patrol cars was broken.
Hundreds of people could be seen on videos posted to social media, some of them standing on top of police cars.
Police quickly realized there were more young people than officers. They reorganized and established a command post to coordinate resources.
Officials said the gathering started as a party but then pictures hit Instagram and hundreds showed up.
"It was body to body, like you couldn't get past the sidewalk at all. There were people crushed together," said Aaron, who attended the event.
Police worried about the safety of the crowd and the neighborhood and worked to protect nearby businesses.
While there were no reports of injuries or arrests, there were fights on the street captured on cellphone video.
"It was pretty in control when I saw it but then it started getting out-of-control. There are a few fights out there, a lot of girls hitting each other," said Ian Rentschler who lives nearby.
Members of the crowd were seen jumping on cars. Authorities said at least four police cars were damaged. Neighbors' cars were damaged as well.
"(My car has) human-sized body dents, because they were standing on top of it," said Rachel Williams. "It was like twelve kids dancing and twerking on top of my car."
Officers from across the city were dispatched. Officers from the 3 to 11 p.m. shift were held over in an effort to manage the crowd.
Highway patrol and emergency response teams worked to disperse the crowds.
A police helicopter flew over the crowd to track it.
"We deployed multiple resources to that area immediately in an attempt to disperse the crowd peacefully, because what you don't want to do is show up and cause more chaos," said Philadelphia Police Commissioner Richard Ross.
Police said the crowd started to break up by 1 a.m. but smaller groups were still walking through neighborhoods, moving onto North Broad Street and Cecil B. Moore Avenue, among other places.
In the end, no injuries were reported and no arrests were made.
There are already future "No Leaving Sober" events posted on social media.