Detectives released surveillance video Wednesday of the incident.
They say a week ago, around 1:00 p.m., the suspect waited for the victim to cash a check inside a store on South Broad Street.
The man followed her for several blocks to the 1300 block of South Juniper.
Police say he then knocked down the woman, took the wallet from around her neck, and ran off.
The woman wasn't hurt.
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.