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.

Hibs trailed Celtic 1-0 at half-time, but the home side hit back through a 27-minute Abi Harrison hat-trick.
Stirling University held Glasgow for 54 minutes before Hayley Lauder, Sarah Crilly and two from Haley Rosen sealed the visitors' victory.
Elsewhere, Glasgow Girls beat Jeanfield Swifts 5-3.
Hearts Ladies against Hutchison Vale was postponed, with a date still to be re-arranged for the tie.
The semi-final draw will take place at Hampden Park on Monday.

The charges were laid in 2014 after a number of women complained to Toronto police that Mr Ghomeshi had been physically violent towards them.
He denies all the charges, saying his actions were consensual rough sex.
If convicted, the 48-year-old - who was sacked by Canadian Broadcasting Corporation (CBC) in 2014 - could be sent to prison for life.
At CBC he hosted the popular arts show Q.
A crowd of reporters and onlookers met Mr Ghomeshi as he arrived at court in Toronto on Monday.
He faces four counts of sexual assault and one count of choking.
A number of women earlier accused him of punching, strangling and battering, and three of the alleged victims later became plaintiffs in the case.
Throughout the investigation, he denied the allegations and later pleaded not guilty to all the charges.
The CBC began an inquiry into Mr Ghomeshi's sexual activities after Canada's Toronto Star newspaper began investigating allegations by an ex-girlfriend that he had engaged in non-consensual, violent sex with her.
After being shown "graphic evidence" that Mr Ghomeshi had physically injured a woman, the broadcaster fired him in 2014.
Two men, who were arrested in connection with the murder of a missing County Antrim man, have been released.
[NEXT_CONCEPT]
Holders Glasgow City and last year's runner's up Hibernian have both made it through to the semi-finals of the Scottish Cup.
[NEXT_CONCEPT]
Canada's former popular radio host Jian Ghomeshi has gone on trial on charges of sexual assault and choking.