It happened around 6:30 Friday night on the 500 block of South Justison Street.
Police say the teens approached a 24-year-old man, struck him several times and displayed a handgun.
The suspects then fled with the victim's property.
A witness called 911 and officers spotted the teens running on the 400 block of North Market Street.
Two of the suspects, a 13-year-old and a 15-year-old were taken into custody and a black pellet gun was recovered.
Police were later able to apprehend another 13-year-old as well as an 18-year-old.
All four teens are facing charges including Robbery, Conspiracy, and Assault.