It's hoped the latest search will lead to a breakthrough in the case.
The 22-year-old was last seen walking home from a Christmas party in the Haddingdon Road area in 2000.
The 3 acre site in Chapelizod in south Dublin has been sealed off and the search is expected to last a number of weeks.
It is understood that the source made a decision to provide the information after being interviewed during a "cold case review" of the original investigation.
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In recent months, gardai have been working to identify a man who was seen outside Trevor's workplace on the night he disappeared.
New evidence was released to the public last April when the then cold-case was re-opened in an effort to finally solve the mystery as to what actually happened to Trevor Deely.
Tragically, gardai have confirmed they've received information claiming Trevor Deely was murdered by a known criminal.
The search is, however, said to be unrelated to the footage.