Inspector Gary McPolin, who is leading the Diarmuid Twomey missing persons investigation, said the four men could have vital information which could lead to a breakthrough.
“Diarmuid was a devoted father, a good, honest, hardworking man who was looking after his elderly parents,” he said.
“We have devoted significant resources to this case but we are launching a final push in a bid to bring him home.”
It is one of three active missing person searches under way in the city.
Insp McPolin appealed for a taxi driver who drove Mr Twomey’s partner Ciara Byrne home in the early hours of Sunday, December 20, and whose first name they have now established is Paul, to contact them.
Despite several appeals, the driver has yet to come forward.
Insp McPolin also appealed to three men who visited Whitechurch Recycling Centre between 6am and 6.30am on the same date to contact gardaí. “We would like to eliminate them from our inquiries,” he said.
Gardaí launched a missing person appeal on December 21 after Mr Twomey, 31, failed to return home to Carrignavar village after a family party.
He had attended his nephew’s 18th birthday party in Bishopstown with Ms Byrne on the Saturday night and they returned to a relative’s house in the Fairhill area later.
Ms Byrne decided to leave just before 3am and Mr Twomey, who wasn’t feeling well, opted to take a taxi later.
Gardaí have established that Ms Byrne flagged down a taxi on the road near Na Piarsaigh GAA club at 2.50am. But Mr Twomey, who left the house a short time later, hasn’t been seen since.
His mobile phone was found in a farmyard in Ballinahina at about 11.30am that day. Search dogs traced his scent through fields to a byroad, but the trail went cold.
Despite exhaustive searches, involving gardaí, the Garda air support unit, coast guard helicopters, civil defence units, Mallow and Fermoy search and rescue units, Cork Missing Persons group, and dozens of local volunteers, Mr Twomey has yet to be found.
Gardaí have established that during her taxi journey home, Ms Byrne and Paul discussed the Syrian refugee issue, they established that Paul knew her mother, and that he had worked previously at Lee Cabs.
Insp McPolin also renewed his appeal to landowners, particularly between the Farm Power Ltd compound and Whitechurch, and along the Old Priest Rd, to check fields, ditches, streams and out-houses.
Anyone with information should contact Gurranabraher Garda Station on 021-4946200.
Meanwhile, gardaí are still coordinating searches for Colin Ronayne, 31, who was last seen on College Road around 6am last Friday, New Year’s Day.
He is described as around 5ft 7in tall, of medium build with short dark hair. When last seen, he was wearing a black V-neck jumper, black tracksuit bottoms, and grey pointed dress shoes.
Anyone with information should contact the Bridewell Garda Station on 021-4943331.
Searches are also ongoing for Thomas Rawley, 63, from Bishopstown in Cork.
He was last seen on South Main Street at around 7.30am on December 22.
He is about 5ft 7in tall, of thin build, with dark hair shaved. He walks with the aid of a crutch.
He was believed to have been wearing a dark navy overcoat, black pants, and baseball cap.
Togher gardaí urged anyone with information to contact them on 021-4947120.