The claims have prompted fears about a social media craze in which pupils are coaxed into sending compromising “selfies” by their schoolmates.
Today, police confirmed that they were investigating an allegation – and urged other victims to come forward.
Officers said they were treating the issue as a “priority” and would give specialist support to victims.
The parent of one pupil involved claimed the issue was “rife” in lower-year groups of secondary schools.
Some pictures are understood to have been sent between pupils of Armadale Academy, Bathgate Academy and St Kentigan’s High in Blackburn, West Lothian.
The concerned mother was horrified to discover that her child, then aged 12, but now 13-years-old, had sent a picture of her cleavage to a male schoolmate.
The youngster was then invited to join a private Facebook conversation in which the revealing photograph was shared with other people, alongside several other compromising pictures of young girls. She immediately removed herself from the group when she saw the images.
Her mum, who asked not to be named for fear of identifying her child, added: “My daughter feels very embarrassed and shocked. This shouldn’t be happening. It’s across the schools in West Lothian. The officer I spoke to said the more people he spoke to, the more he heard about it happening.”
The parent said that other young girls had told her daughter they had been persuaded to send topless or nude pictures to male classmates.
Police have only received one official complaint, however officers are keen to hear from other affected youngsters.
A police spokeswoman said: “Police in West Lothian are investigating following allegations that indecent images of a 13-year-old girl were shared on social media. Inquiries are ongoing and we urge any other victims to come forward.
“Tackling the creation and sharing of indecent images is a priority for Police Scotland, with all complaints received thoroughly investigated. We provide specialist support to victims and target offenders to bring them to justice.”
The parent called for more robust communication between schools and parents to try to keep the children safe.
She added: “The parents should be made aware of this. [The schools] have known about this for months.”
A West Lothian Council spokesman said: “We take the online safety of our pupils very seriously and are currently working closely with police on this matter. Schools and parents both have an important role to play in helping make young people aware of the dangers of inappropriate internet communication.”
The spokesman urged parents to attend Child Exploitation and Online Protection information evenings in schools and youngsters to think carefully before posting online.