Investigators have identified the suspect as 32-year-old Christopher Reeves of South Philadelphia.
He is described as 6'5, 180 pounds, and was last seen wearing a yellow hooded sweatshirt.
Police say at about 6:15 a.m. Thursday, the suspect approached a female employee as she was opening the Bean Exchange Coffee House at the corner of 7th and Bainbridge streets in the city's Bella Vista neighborhood.
He told her he was homeless, police say, and needed a dollar to get back to the shelter. She gave him a dollar and he left.
However, aout 15 minutes later, he allegedly came back, announced a robbery and took $173 from the register.
Police say Reeves then forced the employee into the bathroom and sexually assaulted her.
The victim suffered multiple injuries and was rushed to a local hospital for treatment.
They say Reeves has at least 14 prior arrests for robbery and burglary in the area.
Meanwhile, residents were left shaken by the attack.
"It's horrible. I walk my dog by [there] every day and I stop in there for coffee, that's horrible," neighbor Midge Shull said.
"This is usually considered a pretty safe neighborhood especially since there's a lot of foot traffic and things like that," neighbor Julie Peters said.
The Bella Vista Town Watch group says this attack is far above the fare of petty crime that they usually see.
"There's usually not that many when you add it all up, so this is extraordinary for us and it's as bad as it gets," Greg Pastore of the town watch said.
Police say the suspect should be considered armed and dangerous. If you see him, they say do not approach him and to call 9-1-1 immediately.
Anyone with information is asked to contact police at 215-685-3251 or 215-685-3252. Anonymous tips can also be submitted online at www.phillypolice.com/forms or call the Tipline at 215-686-TIPS (8477).