Ciara Breen went missing from her home in Bachelor's Walk in the town in February 1997.
17 year old Ciara Breen was last seen by her mother Bernadette in the early hours of February 13th 1997.
The pair had gone to bed shortly after midnight, but when Mrs Breen got up to use the bathroom in the night, she noticed that her daughter wasn't in her room.
Bernadette Breen told Gardaí that Ciara hadn't taken any clothes or money with her, and believed she went to meet someone.
She never saw her daughter again.
In April, a man in his 50s from Dundalk was arrested, but later released without charge with a file sent to the DPP.
It's understood the man was known to Ciara Breen, but not related to her.
This morning, Gardaí in Dundalk began a fresh search of land in the town.
Members of the Garda Technical Bureau and a forensic archaeologist are combing a section of land in the vicinity of the garda station, but it's understood nothing has yet been found.
