Authorities have recovered surveillance footage, which they have not released yet, that captures the robbery on camera.
Police say the victim was walking at 22nd and Cambria streets around 8:30 p.m. Wednesday when he was approached by five men.
Authorities say the suspects picked the man at random.
The victim told police the men searched his pockets and took his $20.
Then one of the suspects shot him at point-blank range.
"You can see one male going through his pockets. And that same male, after going through his pockets, put a gun right to his face for some unknown reason and fired a shot," Philadelphia Police Chief Inspector Scott Small said.
The men ran away south on 21st. The only description police have of the suspects is that they were wearing dark-colored coats.
The victim is now stable, but has a bullet lodged in his face.
The violent night continued in Philadelphia. Police are also investigating an unrelated incident in Kensington.
A 30-year-old man told officers he was stabbed in the leg during a robbery around 11:30 p.m. at North 2nd and Huntingdon streets.
He was taken to the hospital in stable condition.
Anyone with information is asked to contact police.