Cops want to track down a well-dressed man who witnesses said masturbated in front of a woman on a Manhattan subway platform on Monday.

Investigators said a 38-year-old woman stood on the southbound N and R train platform at the Fifth Avenue station when she heard a hissing sound at around midnight.

RELATED: Cops look for lewd subway rider on R train

The woman told officers she turned around and saw the unidentified suspect masturbating with his penis outside his pants.

Authorities said the woman began to cry as the man walked away from the station, prompting a second male bystander to ask the woman what happened.

RELATED: Cops arrest man on 5 train for sexually abusing female officer 

The good Samaritan heard the woman's story and started to track down the subway creep.

The man then took his cellphone out and began to videotape the suspect before he left the station.

That's when police said the suspect pulled out a black handgun and told the man to mind his own business before he walked out of the station.

No one was injured, but cops want to track down the man, who was last seen wearing a gray suit with a white-collared shirt.

Anyone with information regarding the suspect or incident can anonymously call the NYPD's Crime Stoppers Hotline at 800-577-TIPS or text their tips to 274637 (CRIMES) then enter TIP577.