Richard went missing aged 27 in 2001 and has not been seen since.
The Doolan family, from Croy in North Lanarkshire, have never lost hope that he might return to them and always make a point of including him in their Christmas celebrations.
"We send him cards," says Mrs Doolan. "His first Christmas card this year has already come in from his sister.
"It was his 40th birthday in June this year and we had a wee cake for Richard here, with a picture of him when he was a wee laddie.
"I miss him terribly. Every day I think about it, every minute. You just wonder and wonder and wonder all the time what's happened to him. I wonder what he would look like now.
"I feel as the years go by there's less likelihood of Richard coming home, but I would like him to."
Richard is one of about 250,000 people who go missing in the UK each year. Slightly more people go missing in Scotland relative to the population than in England and Wales. While nine out of 10 missing person incidents are closed within 48 hours and 99% within a year, some people are not seen again for years or never heard from again.
The charity Missing People, which supports those who are left behind when someone goes missing, is running a campaign, Home for Christmas, to highlight the experiences of families like the Doolans. The charity is supported by the People's Postcode Lottery but also relies on donations to carry out its work, which includes running a 24-hour free, confidential support line.
Chief executive Jo Youle said Christmas often served as a reminder of a family's loss: "One woman told me she looks all around her and it seems like everyone is together with their families. That emphasises the fact her loved one is missing.
"We are a 24/7 organisation. We are here over the whole of Christmas, to be there for families."
When Richard Doolan went missing, there were no clues as to where he might have gone. His wallet and other key documents were still at his flat near the family home, though his mobile phone was gone. He lived by himself, but had spent that day largely with his mother. "When he left here that Saturday, I knew there was something wrong," says Mrs Doolan. "There was an anxiousness about him. He kept coming back up to the house. He came in quite early, around 10am. He was going away home and then came back again.
"Then that night he was going down to an AA meeting and that's the last I saw of him."
Richard, who was not working at the time due to a hand injury, attended the AA meeting. Several people reported seeing him in the next 48 hours and the family went out looking for him, but the trail went cold. "After Tuesday, when there was nothing more, I just felt Richard was gone," says Mrs Doolan. "It felt ominous."
She believes her son may have been depressed and is concerned he had suffered two knocks to the head that had not been seen by doctors. First he banged his head when he fell off his bike, then a few weeks later he and a friend were driving when the car came off the road and went down a ravine. Again he hit his head, but as on the previous occasion declined to go to hospital.
Richard was the fifth of six children born to Jean and Richard Snr, and the only boy. "He was a lovely lad," says his mother. "He was quiet, he played the guitar and was a good singer. He was fine in amongst family but quieter outwith all that."
Richard's sisters stay in touch with police and make a point of contacting them if they hear a body has been found, but have not given up hope that he could return. Mrs Doolan's husband does not discuss his son's disappearance as much as his wife, but the couple do talk about him most days.
Mrs Doolan also prays for him every day. "I've dealt with it by handing him over to God," she says. "People still ask me about him and that's good for me. I know someone who will always give me a tap on the shoulder and say 'No word on Richard yet? Just keep the prayers coming'. I just want people to remember Richard and to pray for him, to pray he's on his way home. I'd like people to remember that Richard could still be out there.
"I used to think he was away and he wouldn't be coming back, but there's always hope."