Michael Tony Lynch, a father-of-four, moved from his home in Magheraveely, Co Fermanagh to a flat across the border in Clones, Co Monaghan in 2001 to work as a digger driver for a drainage company.
Two months later, in January 2002, his family became worried when he failed to turn up for work.
His wife, Angela Lynch, visited his flat to find that all his things were still there but that he had disappeared.
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He was reported missing on January 6 but even his car, a white Mitsubishi Galant, has never been found.
The first in a series of planned searches of lakes and quarries in and around Clones got under way yesterday morning, coinciding with the 18th anniversary of his disappearance.
The fresh searches, which were assisted by an overhead drone, were carried out by An Garda Siochana in conjunction with local members of Monaghan Civil Defence.
A spokesperson for An Garda Siochana, said: “The last known sighting of Mr Lynch was at Fermanagh Street Clones, County Monaghan at 6pm on the 6th of January 2002.
“The investigation into Mr Lynch’s disappearance is ongoing and to date Mr Lynch and his car - a white Mitsubishi Galant registration number TIL4670 - have not been located.
“The purpose of the planned searches is to establish if Mr Lynch’s vehicle may have been submerged at one of these locations.”
Last January, his family made an appeal for information on the television programme Crimecall, broadcast by RTE.
His wife, Angela, recalled the day she went to Tony’s flat in Clones and realised he was missing.
“Every single thing he owned was in that flat,” she said. “It was like he just went out to the shop and just didn’t come back.”
His daughter, Mary, told Crimecall: “Different things go through our head all the time about what could have happened. We just really need some answers.”
Tony’s son Peter said: “During the summertime he used to take me to work with him. I’d sit up on the back of the digger all day with him.”
A spokesperson for An Garda Siochana said yesterday: “Gardaí investigating this missing person case have exhausted a number of leads and at this point are renewing their appeal for information.”