Sandy Davidson was only three years old when he vanished from his grandparents' home in Irvine. That was 40 years ago.

He had been playing in the garden with his sister Donna when the gate flew open and their dog escaped on the morning of April 23, 1976.

Sandy ran after him while Donna rushed to tell their grandparents what had happened. The curly-haired boy was never seen again.

In the four decades since, there has never been a funeral or memorial service for Sandy - and no closure for his loved ones.

He is among more than 50 Scottish children and teenagers reported missing over the last five decades who have never been found.

As the 40th anniversary of Sandy's disappearance approaches, his family has appealed to anyone who may know anything to step forward.

Donna, now 42, said: "I don't think he's still alive, but we still need to find him. We've never had a funeral or a memorial service and we never will until he's found.

"I think someone reached over the fence and opened the garden gate from the outside, which let the dog out and sent us after it.

"Somebody knows something. We've lived with this for so long - it's taken over our lives."

Police Scotland inherited 591 unsolved missing persons cases dating back to the 1960s when it took over from the country's eight regional forces in 2013.

They included 57 missing children and teenagers, some of whom were as young as two years old when they disappeared.

The force handles 35,000 missing persons' enquiries a year, more than 99% of which end with the missing person found safe and well. Seven out of every ten people are traced less than 16 hours after they are reported missing.

But for the families of those few who do not return, their disappearance is often the beginning of a lifetime of loss.

Police Scotland plans to issue a renewed appeal for witnesses this weekend to mark the 40th anniversary of Sandy's disappearance.

Pictures of Sandy will be shown on digital billboards and online in an attempt to uncover new information about the case.

Donna added: "At the time it was a massive search but I think police could have done more to revisit the case in the time since.

"I know we're not going to find Sandy alive but he's out there somewhere and we need to find him. At least then we could lay him to rest."