Three women whose sister disappeared more than 40 years ago say they still hope her remains can be found so their family can be “complete again”.

Mary Duncan went missing as a 17-year-old in West Dunbartonshire in March 1976.

Despite a major police investigation, no trace of the Bonhill teenager was ever found.

Her sisters told BBC Scotland police are planning to excavate land in the area in the search for Mary, who would have turned 60 this Saturday.

Marion McFarlane told the broadcaster: “It would be wonderful for us to get her back, especially at this time.

“We should be having a birthday party, buying balloons and celebrating Mary’s 60th birthday with her and her children and maybe grandchildren.

“That’s a whole generation that is missing from our family.”

Mary Duncan's family
In July last year, Mary Duncan’s sisters Debbie Rennick, left, Mandy Duncan, centre, and Marion McFarlane made a public appeal for information to try and find out what happened to her (PA)

Mary, who had a 13-month-old daughter, vanished after telling her family she was going to meet a friend. Her baby later died of natural causes.

Sister Debbie Rennick told the BBC: “Over the years we’ve come to realise she is no longer alive. But this investigation gaining momentum has given us hope that we might get some kind of resolution.”

Mandy Duncan added: “We just want to finish it and bring her home so our family is complete again.”

A Police Scotland spokeswoman said: “We are not in a position to confirm any details. This is still an ongoing inquiry.”