James 'Jimmy' O'Neill vanished without a trace 10 days before Christmas from his Waterford city home on December 15, 1947.
He was aged just 16 at the time and has never been heard from or seen since - making him Ireland's longest missing people case.
He would now be 90.
The Waterford teenager had lived on Leamy Street in the city and worked for Clyde Shipping Company, which operated between Waterford and Liverpool.
His younger brother Frank says he never came home from work.
"He had a half day and never came home, and apparently my mother had the dinner and all ready for him."
Frank said previously that his brother may have made his way to Liverpool and from there travelled on to New York, but even though an 'SOS' was placed in local newspapers at the time there was never a result.
Frank said his brother’s disappearance devastated his family.
"It broke my parent's heart - both of them - it killed them in the long run,” he said
"It shortened their lives, because even on my mother's deathbed there was one lady said to me - called me that morning - a lady that was in the ward with my mother.
"And she said to me 'Who's Jimmy?', I said 'That's my brother who went missing' and she said 'That's who your mother was crying for all night'".
Jimmy was one of five children in the O'Neill family - alongside a sister Nancy and brothers Jack and Frank.
Another brother Noel died aged six months.
Frank O'Neill's mother and father, Bridget and James, died in 1974 and 1966 respectively never knowing what became of their second youngest son.
Frank’s sister Nancy, who had lived in New York for 36 years but returned to Ireland after her husband passed away, also lived in London between 1952 and 1958.
"She always made enquiries about Jimmy," said Frank. "I was the youngest and never had anyone to grow up with.
"I never married. I saw my late parents' grief - around holiday time, Jimmy's birthday, the day of his disappearance.
"I still have all those days etched in my mind, it's something I can't eliminate. But somebody must know him."
Frank is now 78 but he still hopes to get closure before he dies.
"If there's someone outside, or anywhere, that have any little bit of a description - or anywhere abouts know any knowledge of where my brother's missing - I would deeply appreciate to know,” he said previously.
A Facebook page has been set up as part of the appeal.