Mark Gourley, from the Castlemara estate in Carrickfergus, was reported missing in March 2009. He was last seen in the Burney's Lane area of Glengormley.
In 2013, police investigating the 36-year-old's disappearance said they had begun a murder inquiry.
On Monday, two men, aged 45 and 43, were arrested in Carrickfergus.
The pair were released on police bail on Monday night pending further enquiries.
The body of Mr Gourley, who was described by police as a "vulnerable individual" who had been on medication at the time of his disappearance, has never been found.
Det Insp Darren McCartney appealed to anyone who may have information about Mark's disappearance or who may have seen Mark on or after 7 March 2009 to contact police.
"Previous appeals for information did generate reports of sightings but the last definite sighting of Mark was at 2.30pm on 7 March 2009 in the Burney's Lane area of Glengormley," he said.
"Mark did not have a mobile phone or a significant amount of money with him when he disappeared."
Police said although Mr Gourley was last seen in the Glengormley area, he was from the Castlemara area of Carrickfergus and he may have returned to that area on 7 March 2009.
"Police are asking for anyone who may have noticed vehicles or individuals acting suspiciously in either the Burney's Lane area of Glengormley or in the Castlemara area of Carrickfergus around 7 March 2009 to contact police on the non-emergency number 101," Det Insp McCartney said.
"I believe there are people in these communities who have knowledge of what happened to Mark.
"Additionally, people may have heard rumours about what happened to Mark. I would appeal to them to share this information with police.
"If anyone has information about him, I would ask them to examine their conscience and come forward to police."
Mr Gourley was about 5ft, 9" tall, described as well-built, with fair, cropped hair, and an eyebrow bolt in his right eyebrow.
At the time of his disappearance, was wearing a black, zipped jacket with a grey motif on the back of the shoulders, dark Umbro tracksuit bottoms, black trainers and may have been wearing a blue Glasgow Rangers woollen hat.
Two men, who were arrested in connection with the murder of a missing County Antrim man, have been released.