It happened on February 23 at the K&W Grocery Store located on the 2600 block of South 10th Street.
The male suspect was caught on surveillance entering the store at 1:30 p.m. with a gray mask covering his face.
He pointed a knife at the clerk behind the counter and demanded money and cigarettes.
The robber then fled east on West Shunk Street from 10th Street.
Police describe the suspect as a white male with a stocky build. He was wearing a gray mask, grey gloves, a black jacket and dark colored pants.
Anyone with information should call police at 215.686.TIPS (8477) or text a tip to PPD TIP (773847).
Tips will remain confidential.