A 14-year-old girl killed herself after being bullied on a social networking site, her father has claimed, Leicestershire, England.
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.
And called for tighter controls to be applied to social networking sites such as ask.fm, a question and answer forum.
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."
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 I'm going through rite now.
I have just seen the abuse my daughter got from people on ask fm and the fact that these people can be anoymous is wrong."
On his Facebook page, he asked people to sign an e-petition to introduce safeguarding measures on sites used by children.
Unlike sites such as Facebook and Twitter, there are no options to block or report users on ask.fm.
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.
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.