The incident happened at 11:17 a.m. at the CVS Pharmacy store on West Chester Pike.
Police say the man showed the barrel of a gun from his coat pocket.
He is described as a black male in his 40s or 50s, approximately 5'9 to 6' tall with a thin build.
He fled in what appeared to be a dark- gray Toyota Corolla, last seen headed east on Manoa Road toward Lower Merion Township.
The gray Toyota has a broken passenger side-rear window, patched with plastic secured with white tape.
Anyone with information is asked to contact Detective Matt Hufnal of the Haverford Township Police Department at (610) 853-1298 x 1236.