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Retired detectives are being urged to help cold case officers investigate the disappearance of a teenage girl more than 40 years ago.

Mary Duncan, 17, was last seen in March 1976 when she left home after telling her family she was going to see friends.

Police Scotland’s Major Investigations Team launched a fresh probe last year after new information emerged.

Now the force has asked former officers in the Strathclyde Police Serious Crime Squad between 1976 and 1979 to come forward.

They issued the appeal on social media used by retired officers. One of the sites – Semper Vigilo, Strathclyde Police’s motto – has more than 4000 users.

They were urged to call the Operation Senator incident room in Dumbarton. No details were given. But the Mail can reveal detectives want to speak to officers involved in Mary ’s case.

(Image: Daily Record)

Detective Superintendent Calum Young said: “We are appealing for any officers who worked on the original investigation into Mary’s disappearance to contact us.”

Squad members were based at force HQ in Pitt Street, Glasgow. One retired officer said: ”We helped out local police and CID. We were often called in if an investigation was in difficulties or had hit a brick wall.

“The investigation team will be hoping old cops can recall information that may not be in the files.”

Mary, who would have been 60 this year, disappeared from her home in Bonhill, Dunbartonshire. In April, police searched the former home of her stepfather, jailed sex offender Norman Duncan, half a mile away.

Police have spoken to Duncan, 73, jailed for five years in 2016 for abusing girls aged eight to 15 in the 60s and 70s.

(Image: PA)

Mary had a 13-month-old daughter, Laura, who died after she vanished.

In January, police dug up land in nearby Alexandria.

Police want people who worked at Vale of Leven Hospital in 1976 to get in touch. Mary’s sisters – Debbie Renwick, Mandy Duncan and Marion McFarlane – also appealed for help.

Mary was wearing a navy skirt, black platforms, a green hoodie and a black and white dogtooth check coat when last seen.