The Prime Minister has promised to crack down on cyber bullies.
In a letter to the mother of tragic teenager Izzy Dix, David Cameron pledged to do all he could to end the nightmare of "cowardly bullying" that many school children are exposed to on social media sites.
In a heartfelt, hand-written letter to Gabbi Dix, mother of the 14-year-old Brixham schoolgirl who is believed to have taken her life, the Prime Minister says: "We will do everything we can to put pressure on those that own, run and exhibit on these sites."
Police are investigating the teenager's death amid claims that she was the victim of bullying on a social media website.
In his letter, Mr Cameron attacked "cowardly bullying" on the internet.
"We will do everything we can to put pressure on those that own, run or advertise on these websites," Mr Cameron wrote.
Ms Dix wrote to the Prime Minister about the campaign she is leading for "real change to the way bullying is dealt with in society".
Mr Cameron wrote of his "personal commitment" to ensuring that website owners "take more responsibility for the actions of their users".
He said: "Bullies often mistakenly believe that they are beyond the reach of the law because the abuse that they commit occurs online.
"I am very clear that this is not the case, and that police have the power to investigate it as they would any other crime."
Referring to the death of his severely disabled son Ivan in 2009, Mr Cameron continued: "Whilst I know this will be of scant consolation at this time, I know from my own experiences of losing a child that there will come a day when you will be able to see past the pain to remember the happy times that you once shared together, and the great joy that Isobella brought to those who knew her."
He added in a footnote: "We will do everything we can to put pressure on those that own, run or advertise on these websites."
Ms Dix replied that it was "good to know" that Mr Cameron was aware of the campaign, created after her daughter's death.
Izzy, a gifted pupil with ambitions to go to Oxford University, was found hanged at her home on September 17.