According to Philadelphia police, the attack happened on Dec. 12 at about 6 p.m.
Police said the 20-year-old male victim was entering the SEPTA platform at 1100 Market Street when an unknown male took his wallet and ran onto a train.
"The complainant then followed the offender onto the train. Unbeknownst to him, the offender was with three to five more juveniles who assaulted him on the train," said SEPTA Police Captain R. Kitt Walls.
The incident was caught on surveillance video.
Investigators say the victim was simply trying to get his wallet back from the suspect but ended up getting punched from behind, then kick and stomped after falling to the floor.
Walls says the department is now working to see if this case might be linked to other similar incidents.
"We've had a rash of maybe two or three other assaults by juveniles on passengers within this corridor between 40th Street and 11th Street," he says.
SEPTA officials say they are rolling out new initiatives to improve security, including increased patrols onboard trains.
But some SEPTA customers say they are very concerned that the unfettered violence plaguing the city is spilling over to the transit system.
"I don't feel safe at all. I don't hardly even take SEPTA anymore. I used to take SEPTA every single morning, but I don't any more," said Fayetta Rivers.
Anyone with information about the assault or the suspect is asked to call SEPTA Police.