Gardai, who are investigating the disappearance of Trevor Deely, have sealed off three acres of woodland in Chapelizod in south Dublin, broadcaster RTE reported.
Originally form Naas, Co Kildare, the 22-year-old was last seen walking home from a Christmas party shortly after 4am in December 2000.
Detective Inspector Paul Costello says the search area remains closed to the public.
In April, newly enhanced CCTV footage was released showing Mr Deely talking to a man dressed in black outside the Bank of Ireland on Baggot Street.
The search is, however, said to be unrelated to the footage. He had called into the bank's asset management office on Wilton Terrace, where he worked, in the early hours of the morning.
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Detectives believe this was the same man captured on CCTV following Trevor along Haddington Road afterwards.
Mr Deely then leaves through the same gates carrying an umbrella and stops briefly to fix his jacket.
Gardaí say the search is being carried out after new information, and will attempt to uncover evidence related to the case.
They were also known to have been active in the area of south inner city Dublin where Mr Deely was last seen alive.