A man arrested on suspicion of murdering Kyle Vaughan from Caerphilly in south Wales has been realised from police custody.
The 24-year-old was last seen at his home in Newbridge on December 30 and is now assumed dead.
A 27-year-old man, also from Newbridge, was arrested on Thursday and has been questioned by police since then.
Detectives have also released two other people on bail pending further inquiries -a man, 21, from Newbridge, and the boy, 15, from Abercarn, held on suspicion of assisting an offender.
Their release comes after a 62-year-old Newbridge man was arrested on Saturday on suspicion of perverting the course of justice and later released on bail.
Detectives are continuing to investigate Mr Vaughan's disappearance.
Police family liaison officers were providing support to the missing man's family after they were told last week he is now presumed dead.
They also appealed to the public for any information regarding Mr Vaughan's disappearance.
Concern had been rising for his welfare, as he suffers from diabetes and requires regular insulin injections, for some time.
A Gwent Police spokesperson said it is believed Kyle was last seen on the A467 between Risca and Crosskeys, "some time between 11pm and 11.45pm on December 30th 2012."
They added: "It is believed he was wearing a dark coloured beanie hat, a dark coloured t-shirt, three quarter length denim shorts, white trainers and a gold chain.
"On the same night at approximately 11.45pm, officers found Kyle's car, a silver Peugeot 306, which had been involved in a collision."
Specialist officers have been brought in as part of a major search operation focusing on several areas.
The missing man inquiry had been upgraded to a murder investigation on Friday after the arrest of the 27-year-old man on suspicion of murder.
But despite a nationwide police appeal and a growing online information campaign the whereabouts of the former Cwmcarn High School pupil remain a mystery.
Unilever worker Mr Vaughan is described as 5ft 8ins, of slim build, with short dark hair, and brown eyes.
He was known to wear a gold neck chain with a cross, has a distinctive tattoo of a pair of flaming dice on his inner left forearm and tattoos on his right leg.
Anyone with information should call 101 or Crimestoppers anonymously on 0800 555111.