It's 25 years since Deirdre Jacob went missing in Kildare.
The 18-year-old was last since near her home in Newbridge on the afternoon of Tuesday the 28th of July in 1998.
Gardaí say "an open and active investigation" continues into her disappearance by a dedicated investigation team based at Kildare Garda station.
Mr Jacob, is appealing for anyone with information to come forward.
"We believe that there is a person or persons who has information that would be vital in the investigation.
"We're always hopeful. We always have a positive outlook on that. The information will come forward that will make the difference. We are striving now at the moment to get information as to where Deirdre is so we can actually bring her back".
Deirdre's father, Michael Jacob, says they want closure.
"There's no day that we don't ponder as to what may have happened and you try in our minds to retrace the steps that Deirdre made from Newbridge over that 25 minutes.
"As to what might have happened, was she being watched, was someone trailing her? We just don't know, but you try to figure out that in your mind".