Authorities initially believed the victims had been shot, but later realized they were hurt when they were struck, possibly pistol-whipped.
Investigators say there are different accounts of what happened, so they are still trying to piece it all together.
Police were called around 11:30 p.m. Thursday for the report of a robbery at a home on Hedgerow Drive in Falls Township.
Arriving officers found approximately 12 people, between the ages of 18 and 20, at the house where alcohol was present.
Police say four people were robbed at gunpoint, and two of them were injured.
"Two of the persons robbed suffered some kind of strike to the face, whether from the handgun itself or another object we're not sure at this time," said Lt. Todd Pletnick of the Falls Township Police.
Police say one of the suspects held the gun while the other went through the victims' belongings, stealing a couple hundred dollars, cell phones, wallets and keys.
Most of the partygoers fled in separate vehicles before police arrived. However, a 20-year-old was left behind, and that person allegedly told police that shots were fired.
However, police say, no shell casings were found.
Police are investigating the possibility that the robbers were hanging out at the party beforehand.