Paige Doherty, 15, disappeared from Clydebank in West Dunbartonshire on Saturday.
The popular schoolgirl had been due to catch a bus to her part-time hairdressing job but never arrived at the salon.
The teenager’s body was discovered in a wooded area by a busy roadside two days after she vanished.
On Tuesday, her mother Pamela Munro said the family was “devastated” as police confirmed they were treating the death as murder.
The last known sighting of Paige was at 8.20am when she stopped at a shop selling rolls, having spent the night at a friend’s house nearby.
Police Scotland detectives are attempting to piece together her movements before the discovery of her body more than a mile from the Fleming Avenue shop.
They said she would normally catch the bus from East Barns Street to Glasgow city centre and then travel on to Street Image hairdressers in Kirkintilloch, East Dunbartonshire.
Her mother reported her missing when she failed to turn up at the salon.
Detective Superintendent Duncan Sloan from the major investigations unit said: “Paige was a young, friendly girl with plenty of friends, and for her life to be taken away so brutally at such a young age is unfathomable to everyone.
“We are at the very early stages of this investigation, however I am appealing to anyone who may have any information whatsoever about her movements from when she was last seen in the early hours of Saturday morning to when her body was recovered at lunchtime on Monday.
“It’s crucial that I piece together where Paige went after the sighting at the roll shop and her movements over the course of the weekend and I can only do that by appealing for information from the public.”
Paige’s body was found at around at around 12.45pm on Monday at the side of Great Western Road, a busy route connecting Clydebank and Glasgow.
The area was cordoned off to allow forensic officers to work at the scene. Members of the public have also left flowers and tributes to the schoolgirl by the roadside.
Police have not revealed the nature of the injuries and a post-mortem examination was due to take place.
Mr Sloan said he was “open to all motives” over the attack.
The detective said: “From speaking with family and friends, it is apparent that Paige was a well-liked, popular girl with many friends, who was keen to finish school and go on to work.
“She independently secured a work placement at a hairdressing shop and would travel by bus into Glasgow city centre and then travel on another bus from Buchanan Bus Station out to Kirkintilloch. Someone may have seen her in this area at the time.
“I am also particularly interested in hearing from anyone who may have seen anyone acting suspiciously in the area where she was found off Great Western Road on Monday lunchtime.
“This is a particularly busy route with lots of cars and buses passing, walkers and joggers on the pavement. Perhaps someone saw a vehicle in the area or people acting out of character or acting unusually – that could help us in the investigation.
“Any information, however small, may help this investigation.”
Posting on Facebook, the teenager’s mother wrote: “We are absolutely devastated, as many people who know her will be xxx.”
Laura Mason, chief education officer at West Dunbartonshire Council, said: “Paige was a bright and popular pupil with a good sense of humour.
“We are doing everything we can to support our young people at this sad time.”
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