It was around 8:50 p.m. Thursday when two women, a 52-year-old and a 57-year-old, were walking in the 1000 block of East Mount Airy Avenue.
The women were approached from behind by an unknown man who said "may I ask you a question."
When they turned around, police say the man motioned as if he had a gun and said "give me what you got."
One of the women gave him $20, police say, and the suspect then asked them if they had cell phones.
They said they did not, so the man fled on foot.
Police released surveillance images of the suspect that were taken at a Getty mini-market just before the robbery.
The suspect is described by police as a black male, 20-30 years-of-age, 5'11" tall, thin build, beard, wearing a gray hooded sweatshirt, dark colored pants and dark colored sneakers.
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.