last seen: Having lunch at home on Thursday October 23, 1986.
Went missing: Walking back to Colaiste Eanna secondary school in Ballyroan.
Clues: Philip's school bag was located by two girls in a lane close to his house six days after his disappearance. The lane had already been searched, and the bag was not there at that time. The school bag was thought to hold vital clues, but nothing is known of how it came to be in the lane.
Family: Mum Alice Cairns has said: "We still have hope. We have to have hope. What do you do without hope? Please God sooner rather than later there can be some development."
last seen: On CCTV footage at Baggot Street Bridge in the early hours of December 8, 2000.
Went missing: After an office Christmas party.
Clues: A poster of Trevor appears on lamp posts every December and his family continue to appeal for clues or information.
Family: Dad Michael Deely has said: "We're living in hope. I now have seven grandchildren, whom Trevor has never met, from my three other children. And my dream is for Trevor to meet them."
from: Clare Hall, Dublin 17.
last seen: New Year's Day, 2008, in Spain. At 10pm, she said goodbye to friend Ashley Rose, with whom she had been babysitting.
Went missing: After leaving her friend's house in Mijas Costa in Malaga.
Clues: Eyewitness allegedly saw Amy out with an older man on the night before she disappeared.
Family: Mum Audrey Fitzpatrick has said: "I panic if I go anywhere, or travel, because I think she might build up the courage to come back and I won't be there."