Gardai have opened a new investigation into the disappearance of Trevor Deeley.
The 22 year old went missing after his Bank of Ireland Christmas party in the city on the 8th of December in 2000.
Detectives are to re-interview people and review CCTV in the hope of unearthing some new information which could solve the mystery of his disappearance.
Video footage of Trevor's last known movements is being sent to specialists in the UK for detailed forensic examination.
Lauren, the 9 year old niece of Trevor Deely, attending the second annual Missing Persons Day ceremony at Farmleigh House in the Phoenix park in 2014.
It comes as people gather in Dublin today for a ceremony to remember all those who've gone missing.
Amongst them will be Josephine Pender. Her daughter Fiona went missing 20 years ago from her home in Tullamore in Co. Offaly. The 25 year old was pregnant at the time.
Her mum says there isn't a day that goes by when the horror of it all doesn't hit her.
"I can't see it ever getting any easier. Her baby would be 20 now and probably going to college this year."