Police in the North fear a right hand man jailed loyalist leader Mr Johnny Adair has been murdered in a re-ignition of the UDA feud.
Mr Alan McCullough (21) has not been seen since he was driven from his home in the Lower Shankill area of Belfast last Wednesday night with two men.
He had been among those from the Ulster Defence Association's notorious C Company which fled Northern Ireland under threat of death during the UDA feud earlier this year.
But he returned to his home in the Shankill within the last fortnight, said Detective Chief Inspector Will Kerr who said he believes his disappearance is linked to the feud.
"I think there is a paramilitary connection, we are concerned about Alan's safety, at this stage we would have a belief that Alan may have been murdered," he said.
Police had a significant number of officers involved in the search for Mr McCullough, he said, adding that he was considering escalating the investigation to a murder inquiry.
A two-day search for a body by police divers in a reservoir at Waterworks Park in north Belfast was called off tonight after nothing was found.
Police had gone to the area after reports of "suspicious activity". Other searches had been carried out and more would continue, DCI said.
Four people, including a top member of the mainstream UDA which forced the Adair faction to flee in February, were released today from police custody without charge after being questioned for more than 24 hours.
DCI Kerr said: "There may be more arrests in the near future."
Northern Ireland's chief constable Hugh Orde said in an interview today that he did not believe the loyalist feud was over.
"Just because you've solved one turf war does not mean another one won't crop up. I think even within the UDA the feud is not over - I am not convinced," he said.
Four people died during the UDA feud which saw Johnny "Mad Dog" Adair returned to jail when his early release parole was ended for the second time when he tried to wrest control of the UDA from those in charge.
After he was back behind bars the UDA leadership warned his C Company followers to get out. They fled on an overnight ferry to Scotland and scattered across Scotland and England.
Adair's wife Gina was among those who, together with Mr McCullough, went into exile. They were warned that if they ever returned they would be shot dead.
In April there was a gun attack on the house in Bolton where Gina Adair had taken refuge. Mr McCullough had pleaded with UDA bosses to be allowed to return to his home and sought assurances he would be safe.
But as one loyalist source said: "Only a fool would have returned without having their safety guaranteed. "Why did he return ? - Its his home and he couldn't stay away."
Mr McCullough's family tonight remained silent about his disappearance, but DCI Kerr said they were "very distressed".
PA