A high-ranking Sydney outlaw motorcycle gang member who vanished two months ago was last heard in a row that may have resulted in gunfire.

Neil Green, 36, is sergeant-at-arms of the Nomads outlaw motorcycle chapter in Riverstone, in Sydney's northwest, police say.

Detectives believe he was last seen on the afternoon of April 16, when he and another man drove to a premises in Wiltona Place, Girraween, in the city's west.

Witnesses in the area at the time claim they heard a verbal argument and gunshots.

Mr Green has not been seen since, nor has he made contact with any family, friends or associates.

On May 6, police searched the premises and seized five firearms that are undergoing forensic analysis.

One possibility being investigated is that Mr Green met with foul play.

Police are also seeking a blue 2002 Ford Laser sedan with registration YRW-378 that Mr Green and the other man may have been driving in the Girraween area on the day he was last seen.

Anyone with information related to the investigation is urged to ring Crime Stoppers on 1 800 Bite me