Raonaid Murray, 17, was last seen alive at approximately 11.20pm on Friday September 3rd, 1999, as she made her way home from Dun Laoghaire town centre.
Her body was found at Silchester Crescent, Glenageary at 12.33am on Saturday September 4th.
She was found less than 500 yards from her home.
In a statement the Garda said many who were then the same age as the teenager are now parents themselves.
“We would ask them to reflect now with the benefit of maturity and hindsight on any information which may be of assistance to the investigation,” they said.
“Despite a large number of suspects having been identified during the course of this investigation, there is in reality no prime suspect.
“The lack of a prime suspect largely arises from the fact that there has been no motive identified in this case. In over 4,500 witness statements there is not one word of enmity towards Raonaid.
“If any person has any information which could assist in identifying a motive for the murder of Raonaid and/or if any person has any doubts about the truth of an alibi already provided, we would appeal for your immediate assistance.
“You may unknowingly be shielding a killer.
“The solving of this murder is of the utmost priority for An Garda Siochana and any information received will be treated with absolute confidentiality.
“The Garda investigation team wish to again thank the public for the invaluable assistance provided in this ongoing investigation to date.”
