Honolulu firefighters suspended their search Thursday for a diver lost at sea, after four days without further sign of the man.

Matthew Curley, 28, was reported missing Monday when a scuba dive tour regrouped and couldn’t find him about a half-mile off Waialae-Kahala.

The Honolulu Fire Department and the Coast Guard launched a search, but the Coast Guard called its efforts off Tuesday night.

The Coast Guard searched from Barbers Point to Honolulu Harbor.

Firefighters extended their search from Makapuu to Rabbit Island. Divers with the department searched underwater and firefighters on Jet Skis and surfboards checked rocky coastlines inaccessible by foot.

Firefighters called off the search about 6:30 p.m., said Honolulu fire Capt. Terry Seelig.

Seelig said the family expressed appreciation for the search, but still has questions about what happened. The Coast Guard is investigating.

Curley is a third-year postgraduate resident in emergency medicine at St. Luke’s-Roosevelt Hospital, according to the NBC News website. He graduated from Bucknell University and New York Medical College.

Island Divers assisted in the search and on Tuesday found a fin that belonged to the company in the water about a mile from the dive site. The fin matched the type and size Curley was wearing, Seelig said.

On Wednesday, the Fire Department searched by boat and helicopter about three miles from shore as firefighters searched the shoreline from Koko Head to the mouth of Honolulu Harbor. Divers with the department also searched underwater for about two miles along the coast.

The Associated Press contributed to this story.