Tony Lynch from Fermanagh was last seen on Fermanagh Street in Clones, County Monaghan, on Sunday, 6 January 2002.
The father-of-four, who was 54-years-old and originally from Magheraveely, had recently moved to Clones.
His family became concerned when he did not turn up for work that week.
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In a release a Garda spokesman said Mr Lynch was reported missing on the 9th of January 2002.
The statement adds: "To coincide with the 18th anniversary of his disappearance Gardaí in Clones in conjunction with local members of Monaghan Civil Defence will conduct a series of planned searches of lakes and quarries in the Clones area."
They say 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.
"The planned operation will begin on January 2, 2020, and will include the use of a drone which can guide Gardaí and the Civil Defence team to locations of interest in the search.
"Gardaí investigating this missing person case have exhausted a number of leads and at this point are renewing their appeal for information. Anyone who may have had sight of this vehicle and/or Mr Lynch since January 6, 2002 is asked to come forward.
"They are also anxious to speak with any landowners who may have noticed a car abandoned on lands or submerged in waters which may fit the description of Mr Lynch’s white Mitsubishi Galant car.
"Those with information are asked to contact Gardaí in Clones on (047) 51028, the Garda confidential line 01-800-666-111 or any Garda Station."