Not knowing where a loved one has gone is agonising on any day.
But perhaps no time is more difficult than Christmas for the families of missing people.
Billy Davies, from Mountain Ash, Rhondda Cynon Taff, went missing on 18 February, 1997 and his family still do not know what happened to him.
It was thought that the 16-year-old, who told his sister he wanted to join the Army, had waded into the River Cynon - despite his fear of water.
His sister, Michelle Davies, 49, said she received a phone call to say Mr Davies had not come home, and so went down to the river.
However, she could find no sign of him next to the water.
"I picked a stick up and put it in the river - it ripped it out of my hand," she explained.
"He would never have gone in there, he was so afraid."
South Wales Police confirmed the case is still open but there were no new lines of enquiry.
Mr Davies' niece, Anna Davies, 31, said Christmas was "broken" for the family.
"You make do with it, you do Christmas - you make the best of it, for the children that are around now," she said.
"It's supposed to be a happy time of the year isn't it, but it's that one seat missing… You're never going to get that back.
"You're sat there thinking what ifs, what could have been, and what would have been now."
Speaking of the effect it had on his mother, Jennifer, who passed away, Michelle Davies said: "Her life ended the day that Billy went missing."
Watching her mother struggle with the loss of her son during Christmas and New Year was painful for the family, with the tormented mother just wanting to be left alone.
Michelle Davies now believes her brother is dead, and has had his name engraved on their mother's tombstone.
She said she decided Mr Davies had died on his 18th birthday.
"I just stood in Porthcawl by the sea and I just broke down crying, thinking 'No, he would have been home by now'.
"He wouldn't have been away that long."
Having a family member vanish without a trace without knowing why is something that Bronwen Vearncombe has endured.
Her brother, Gomer Wyn-Roberts, was in his late 20s when he did not turn up to Bronwen's wedding in north Wales, where he was supposed to be an usher.
He had always been a free spirit, but his parents - who lived in Conwy - never heard from him again.
It was only years later when she was searching his name on Google when she saw an article announcing that he had died aged 53 in London, and his friends were looking for his family.
Ms Vearncombe, 54, who said Mr Wyn-Roberts died of natural causes, explained her disbelief when she read what had happened to her brother: "It was shocking actually.
"I think I'd always hoped that I would find him before we were old enough to be in that situation of dying."
The emotional strain of not knowing where the keen rugby player - known as a "gentle giant" - had gone was heightened at Christmas.
"The festive period is always a challenge, because there's always that place at the table which isn't filled", Ms Vearncombe explained.
She added that it was difficult for her mother to discuss: "My mother particularly never wanted to talk about it, so after a couple of years she sort of pushed it away, whereas my father and I would talk about it."
To this day, Ms Vearncombe does not know why her brother left, but she wishes he could have got in contact to give her parents peace of mind.
"I think something happened around that time that he couldn't face the family or maybe it was some debt - maybe he got into trouble for something.
"I think maybe he thought it would be difficult from his point of view, and the longer you leave it the harder it is to come back."
If her brother was still alive, she knows what she would say to him: "I would say I don't need to know why, I just would love to have a relationship as brother and sister - could we start again, clean slate?
"You don't need to tell me what's gone on it the past, I'm not judging you at all. You've got a niece and a nephew who would love to have an uncle."