The suspect has been identified as 25-year-old Michael Hamilton with a last known address in Norristown, Pa.
The robbery happened at 1:30 p.m. at the Sovereign Bank branch at 2 Aldwyn Lane in the Villanova section of Radnor Township.
Police say Hamilton entered the bank and presented a demand note to a teller. The note demanded money indicated Hamilton was in possession of a weapon.
Hamilton was given $1,400, police said, before he fled on foot.
There were no other customers in the bank at the time and no employees were harmed.
Hamilton is described as a white male standing 5'11" tall with 'scruffy' facial hair. He was wearing a gray hooded sweatshirt underneath a dark jacket, Aeropostale sweat pants and white sneakers.
Police say Hamilton escaped from a work release program on the morning of the robbery. He was serving time in the Montgomery County Prison on a burglary charge.
Hamilton has a lengthy criminal record. Last February he was arrested three separate times for incidents only days apart. In October, he was picked up on burglary and I.D. theft charges and sent to prison.
At the time he was living in a town house in West Norriton. The man who answered the door at that house only said "no comment" on Wednesday.
Hamilton's sister said, over the phone, that the family is worried for Hamilton's safety.
Anyone with information is asked to call Radnor Township Police at 610-688-0503.