Choking back tears as she laid a wreath on the steps of Stormont, Dympna Kerr pleaded for someone to help end their 41 years of torment.
She said: “It is hurtful.
“We have had information and we have had digs but there is something missing.
“All we want is somebody to just make that phone call and give us that last little bit of information.”
Columba McVeigh, from Co Tyrone, was kidnapped in Dublin in November 1975.
Despite extensive searches at Bragan Bog in Co Monaghan, including a five- month excavation in 2013, his body has never been found.
Ms Kerr added: “Forty-one years ago on Halloween night Columba was taken out of a pub in Dublin.
“And that’s it, he has never been seen since.
“It is the not knowing that is the worst. Everybody has lost a close relative in their life – you grieve them and bury them and then you move on with your life. But we can’t move on because we haven’t buried him yet.
“If he was buried it would bring some completeness.
“We just want to get the last bit of crucial information over to the people who will do the dig and go out and find him.
“We want a Christian burial for him in the grave with my mum and dad. That was my mum’s wish.”
Ms Kerr was among dozens of Disappeared relatives who took part in the annual All Souls’ Day silent walk to remember the 17 people who were abducted, killed and secretly buried by republican paramilitaries during the Troubles.
The solemn procession and wreath laying ceremony, now in its 10th year, aims to highlight the cases of those still to be found.
They walked from Carson’s Statue to the steps of Parliament Buildings where Ms Kerr laid a black wreath, with attached white lilies representing those still missing.
Among the sombre crowd walking in the autumnal sunshine were some of the 10 children of Jean McConville, who was snatched from her home in Divis flats in 1972.
The sisters of Brian McKinney who vanished in 1978 also took part for the first time.
Their mother Margaret, now 84 and too frail to walk, first raised the plight of the disappeared when she met US president Bill Clinton at the White House in 1998.
A transcript of a telephone conversation between Clinton and the then prime minister Tony Blair released earlier this year revealed the former president had been so moved by her story that he pushed for the Disappeared to be key focus for the peace process.
Mr McKinney’s remains were found in Co Monaghan in 1999.