It happened on October 28 inside the store on the 3300 block of Aramingo Avenue.
Click here to watch the surveillance video
Police say the suspect walked into the store around 8:35 p.m. When the cashier asked him for help, he said no and left.
The robber waited outside for a few minutes until the employee walked away from the counter to make coffee before re-entering the store.
That's when he jumped behind the counter and grabbed several packs of cigarettes.
As he tried to leave the store, surveillance video captured the clerk trying the block the doors.
The suspect can be seen fighting back with the man, punching him several times in the face.
When the employee backed off, the robber quickly grabbed several packs of cigarettes that had fallen onto the floor and fled the scene, heading west on Westmoreland Street.
Police describe the suspect as a white male, 40-years-old and 5'11" tall with a thin build. He was wearing a grey hooded sweatshirt, gray sweatpants, orange shirt, and a black skull cap with yellow writing.
Anyone with information is asked to call police at 215.686.TIPS (8477) or text a tip to PPD TIP (773847).