Gerry Evans was last seen in Monaghan in 1979
Investigators who were given a map in connection with the search for the body of one of the Disappeared have appealed for more information.
The Independent Commission for the Location of Victims Remains is trying to find the remains of Gerry Evans, 24, from Crossmaglen.
The commission seeks to find the remains of those secretly buried during the Troubles.
Mr Evans was last seen hitch-hiking in County Monaghan in March 1979.
No-one admitted responsibility for his death.
His aunt was given a map in March claiming to identify the location of his body.
Frank Murray, of the commission, said it was critical to their efforts that anyone with new information gave it to the commission.
"These are complicated and difficult investigations and fresh information is crucial," he said.
"For example, the commission currently has a map of a forest area close to Castleblayney which claims to know the whereabouts of the body of Gerry Evans.
"We're currently working on that and following it up but any additional information in this case would help us to fine-tune our search and improve the chances of recovery."
Mr Murray and fellow commissioner Sir Ken Bloomfield have reported to the British and Irish governments that the current phase of scientific investigations is due to be completed before the end of next year.
In an appeal for fresh information, they insisted that no excavations of sites would take place unless there was a good prospect of success.
Sir Ken said every possible lead was being investigated and areas, often of bogland or other difficult terrain, were being surveyed by a dedicated team.
"It is both disappointing and frustrating that this work has yet to yield positive results, but it will continue until we are satisfied that everything possible has been done to obtain information and act upon it," he said.
Mr Murray added: "Any new information received by the commission could be the final piece in a jigsaw which helps our investigators locate the remains of a loved one."
The IRA admitted in 1999 that it murdered and buried nine of the Disappeared - Seamus Wright, Kevin McKee, Jean McConville, Columba McVeigh, Brendan Megraw, John McClory, Brian McKinney, Danny McIlhone and Eamon Molloy - in secret locations.
The bodies of four - Eamon Molloy, Brian McKinney, John McClory and Jean McConville - have been found.
Others who vanished during the Troubles include Mr Evans, Charles Armstrong, Robert Nairac and Seamus Ruddy, who disappeared in France and whose murder was admitted by the INLA.