A 14-year-old Leicestershire girl killed herself after being bullied on a social networking site, her father has claimed.
Hannah Smith, from Lutterworth, was found hanged on Friday.
Her father Dave Smith, wrote on Facebook that he found bullying posts on his daughter's ask.fm page from people telling her to die.
Latvia-based ask.fm allows users to post anonymously. An inquest into Hannah's death has opened in Leicester.
Writing on Facebook last Friday, Mr Smith wrote: "Just to let all my friends know my youngest daughter took her own life last night."
He adds: "Rest in peace my baby and you will never be forgotten xxxxxxx."
The question-and-answer site was set up by two Latvian
brothers, Ilja and Mark Terebin, as a rival to Formspring
in 2010 but has now eclipsed its predecessor.
Members can ask others questions and then get replies,
which include text, photos and videos - via its website
Ask.fm had 13.2 million daily visitors worldwide in June
with each one spending nearly six minutes on average
on the site, according to internet research firm Comscore.
It said that made the social network's web domain the
79th most popular in the world.
Ask.fm says users must be at least 13-years-old to join
and requires them to provide a valid name and email
address when they register, although reports suggest
younger children sneak through using fake credentials.
One of its most controversial features is the ability for
members to pose questions to others anonymously.
Ask.fm's terms and conditions say members should
never use the feature to ask things that are mean or
hurtful, and it allows users to opt out of receiving
anonymous questions via their privacy settings.
However, safety campaigners have said many youths
do not know how to do this.
The network also allows users to report abuse and says
it may hand over identifying information to law
enforcement if necessary.
But in June, Le Monde newspaper reported the service
only had 50 external moderators which it contrasted
with the 30 million questions and answers posted to
Ask.fm every day.
Even so parents might wish to note that Ask.fm warns
members they use the service "at your own risk" and
that it says it bears no liability for content they might
find to be objectionable or obscene.
He added: "My heart is broken in 2 and is gonna take a long time to repair i just hope that none of you have to go through the pain im goin through rite now [sic]."
Mr Smith has called for tighter controls to be applied to social networking sites such as ask.fm.
He wrote: "I have just seen the abuse my daughter got from people on ask fm and the fact that these people can be annoymous is wrong [sic]."
On a Facebook page set up in memory of his daughter, he asked people to sign an e-petition to introduce safeguarding measures on sites used by children.
The page now has nearly 30,000 "likes".
'Loss to understand'
The petition states: "Please sign if you would like the Government to step in and insist that Ask.fm and similar sites help us protect our young people. They are able to join from the age of 13 and can post anonymously."
In a statement, Hannah's headteacher at Lutterworth High School, Nora Parker, said: "The governors, staff and students of Lutterworth High School were deeply shocked and saddened to learn the news that on 2 August Hannah Smith, a year 9 student, took her own life.
"Hannah, who just completed her final year at the school and was looking to transfer to Lutterworth College in August, was a bright, bubbly, popular and thoughtful girl who was liked and respected by all those she came into contact with.
"She had everything to live for and her family, who are utterly devastated, are at a loss to understand why this has happened."
Peter Wanless, chief executive of the NSPCC, said: "This is a tragic case where Hannah felt like she had no other option but to end her life.
"The cruel nature of cyberbullying allows perpetrators to remain anonymous and hide behind their screens.
"This is something that must be tackled before it gets out of hand. We must ensure young people have the confidence to speak out against this abuse, so they don't feel isolated and without anywhere to turn."
The Department for Education said in a statement that no-one "should have to suffer the fear and victimisation of bullying".
"The law is clear that what is illegal off-line is also illegal on-line.
"Perpetrators of grossly offensive, obscene or menacing behaviour face stiff punishment.
Hannah's father told the BBC's Sian Lloyd that he was
both grieving and angry
"Through the UK Council of Child Internet Safety we are working with social networking sites and internet providers to make the internet a safer place for a young people."
It also added that under the new curriculum children would be taught from the age of five "how to stay safe online, and how to communicate safely and respectfully".
At the opening of the inquest into Hannah's death, Leicestershire Coroner's Court was told a post-mortem examination had so far proved inconclusive.
Leicestershire Police confirmed a computer and mobile phone had been secured on behalf of the coroner.
A spokesperson said there was no ongoing criminal investigation, adding: "We await the coroner's verdict before making a decision on whether to pursue that."
The inquest was adjourned until a later date.
The BBC contacted ask.fm for a comment and are still awaiting a response.