It happened at the 19 Degrees Cafe on the 1800 block of Christian Street.
Police say the suspect walked into the cafe just before 10 a.m. and pointed a handgun at the employee behind the counter, demanding money.
VIDEO: Click here for the surveillance video
He got away with an undetermined amount of cash before fleeing on foot south on 19th Street towards Washington Avenue.
The suspect is described as a white male, 5'6"-5'7" tall. He was wearing all black clothing, half-face ski-mask, black hooded sweatshirt with a decal on the back printed in pink and green graphic lettering "Hollywood California", black wool hat, black gloves and armed with a handgun.
Anyone with information should call police at 215.686.TIPS (8477) or text a tip to PPD TIP (773847).