Investigators say shortly after midnight, the teens headed up South Street onto Broad Street and traveled north on Broad.
One police source says some in the crowd assaulted several people along the way. One person was also reportedly robbed.
Police arrested at least three people and got help from SEPTA.
Lt. Gerard McShea told Action News, "There was a little issue. SEPTA did respond quickly by sending buses up. The Broad Street Subway, at that time, had closed for the night."
Police say they were prepared to deal with huge crowds along South Street. They are not calling this latest incident a flash mob.
