Police are searching for a man who sexually assaulted and robbed a woman at knifepoint in Center City this week, after luring her to a remote area under the pretext of helping her find her roommate.

The 24-year-old victim told police the man choked and assaulted her in a grassy area near 15th and Vine Streets, said Philadelphia Capt. John Darby. She was not seriously injured.

The suspect took cash and a debit card, and demanded the victim give him her PIN number. The man then went to two Center City banks to make withdrawals, where a camera at one ATM captured clear images of his face.

The victim told police she and her roommate had been out near a residence at 15th and Locust Streets on Monday night when they lost track of each other. The victim returned to the area sometime before 3 a.m. to look for her roommate and was approached by the suspect, Darby said. The suspect convinced the victim that he knew where the roommate was, and that he had seen the two women out together several hours earlier.

"This male gains this woman's confidence by actually describing what she had been wearing earlier," Darby said. "That is disconcerting."

Together they walked to 15th and Vine, where the assault took place. Afterward the man left on foot.

By the time the woman called police to report the assault, around 3 a.m., the suspect was already making withdrawals from her bank account.

Darby described the suspect as a black man in his late 30s to early 40s, about 5-foot-10, 180 pounds with a "scruffy" face and short black hair. He was wearing jeans, sneakers and a blue or black sweatshirt at the time of the assault.

"We're asking the public to take a look at this guy," Darby said.

The victim has identified the suspect from the surveillance photos, Darby said.

Anyone with information is asked to call the Special Victims Unit at 215-685-3251.

Contact staff writer Allison Steele at 215-854-2641 or asteele@phillynews.com.