Downing Street has released this picture of the letter the Prime Minister wrote to Dave Smith, the father of teenager Hannah Smith who committed suicide after alleged online bullying.
Mr Cameron said he was grateful "as a parent" to Mr Smith for highlighting the problem of bullying on social sites and insisted legislation exists to deal with online trolls.
He reportedly wrote: "I want to reassure you that the Government takes this issue very seriously. There is already legislation in this area".
The father of Hannah Smith, who committed suicide after being bullied on the Ask.fm website welcomes the site's new cybersafety measures.
Major organisations have withdrawn adverts on social networking site ask.fm following the suicide of teenager Hannah Smith.
Maybe it's time we all had a reality check, to look up from our screens, lose the masks we all wear online, and look at each other.