Mark Gourley, 36, from Carrickfergus, went missing on March 7, 2009.
He was last seen in the Burney’s Lane area of Glengormley.
A 45-year-old man and a 43-year-old man were both arrested in the Carrickfergus area on Monday and later released on police bail pending further enquiries.
Police launched a murder investigation in 2013 but the victim’s body has not been located.
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Detective Inspector Darren McCartney said: “Mark was a vulnerable individual and was on medication at the time of his disappearance.”
He did not have a mobile phone or a significant amount of money with him when he vanished.
Mr McCartney added: “I believe there are people in these communities who have knowledge of what happened to Mark.
“Today’s police activity is proof that police are continuing to investigate what happened to him.
“Additionally, people may have heard rumours about what happened to Mark.
“I would appeal to them to share this information with police.”
Mark was from the Castlemara area of Carrickfergus and may have returned to that area on the day he went missing, investigators said.
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 them.