Sgt. John Solecki says detectives are looking at video from surveillance cameras and bystanders who posted footage of Wednesday's brawl on Facebook.
The Reading Eagle reports the teens were fighting at basketball courts in a park when police responded around 4 p.m. Wednesday.
At least one person, a 17-year-old boy, was taken to the hospital and was later released.
Investigators say the large fight involved 75 to 100 teenagers and they scattered when police arrived, but the violence resumed minutes later.
Solecki says police are trying to identify everyone involved, especially those holding weapons. It wasn't clear what started the brawl.
Information from: Reading Eagle, http://www.readingeagle.com/