It happened just before 6 a.m. at the restaurant located on the 1500 block of JFK Boulevard.
Police say the suspect walked into the restaurant and approached the clerk behind the counter.
He handed the 22 year-old woman a demand note and threatened to shoot her.
But the clerk refused the suspect's demands and handed back the note.
The robber then fled empty handed in an unknown direction.
Police describe the suspect as a black male, 40-50 years-old, 5'8" tall and 180 lbs. He was wearing tan pants, a dark colored jacket and glasses.
Anyone with information should contact police at 215.686.TIPS (8477) or text a tip to PPD TIP (773847).