The incident happened around 11:40 p.m., in the single-occupancy bathroom at the Christopher Street bar. The victim, 25, told police she was in the bathroom when the suspect said he needed to wash his hands.
According to the victim, the suspect then sexually assaulted her.
She then called police and was taken to Lenox Hill Hospital for treatment.
Police say they're looking for a man who is 5-foot-10 and weighing around 250 pounds. He had a goatee and was last seen wearing a grey suit.
Anyone with information is urged to call the NYPD Crime Stoppers at 1-800-577-TIPS. The public can also log onto the Crime Stoppers website or text their tips to 274637 (CRIMES) and then enter TIP577.
All calls will remain anonymous.