The family of missing Dublin schoolboy Philip Cairns have made a fresh appeal for the public's help in solving the case.

Tomorrow marks the 20th anniversary of the day the 13-year-old disappeared while walking back to school in south Dublin.

Speaking on behalf of the family, Philip's younger brother Eoin appealed for anyone with information about his brother’s disappearance to get in contact with gardaí in confidence.

Eoin was 11-years-old when his only brother disappeared.

He said: 'He was my best friend.  We played soccer in our back garden, and with other boys on the road.  Philip played hurling for a local team, and he loved to go fishing with my Dad.'

Eoin described how the last 20 years have been extremely difficult for him, his parents Alice and Philip Snr, and his sisters Mary, Sandra, Helen and Suzanne.

'Philip is always there in the sense that he is not there.  At Christmas, birthdays, weddings and other family occasions we think of how Philip should be with us.'

He left his home at Ballyroan Road in south Dublin to return to his new school, Coláiste Éanna, in Rathfarnham, but he never made it back to the school.

Despite extensive investigations, which are ongoing, no trace of Philip has yet been found.

But there is a potentially crucial piece of evidence in the case.

Six days after Philip's disappearance, his schoolbag was found in a laneway near his home.

The laneway links Anne Devlin Road and Anne Devlin Drive.

Detective Sergeant Tom Doyle has appealed to the person who left the bag in the laneway to get in contact.

He said: 'The person may have been a child who found the bag elsewhere. That child is now an adult and perhaps has a family of their own. 

'Or the bag may have been found by an adult at some location and brought to the laneway. It is so important that that person comes forward.  We need to find out where they found the schoolbag.'

Gardaí have told RTÉ News they believe advances in forensic science could yet reveal the identity of people who handled Philip's schoolbag.

Det Sgt Doyle added: 'The bag contains what is called "Touch DNA". Over the coming years, we hope a DNA profile can be established to identify people who came in contact with the bag.'

'I am also appealing directly to the person or persons responsible for Philip's disappearance to get in contact with us at Rathfarnham Garda Station at 01 6666500.'

Meanwhile, Philip's family will gather with the local community later today for a special mass to remember Philip.