The robbery happened at 2:38 a.m. on January 1st at the store located at 5800 Rising Sun Avenue.
Surveillance video released by police shows the suspect walking behind the counter and putting the knife to the worker's back.
That employee then opens the cash register, handing over the money to the suspect, who then flees on foot.
The suspect is described as a white man, about 20 years old with a thin build. He was wearing gray sweat pants, a white hooded sweatshirt, a mask over his face and was armed with a large knife.
Anyone with information is asked to contact Philadelphia Police at 215-686-TIPS (8477), text a tip to PPD TIP (773847) or through PhillyPolice.com.