Social networking websites that don't "step up to the plate" and tackle online abuse "should be boycotted", says prime minister David Cameron.
Cameron told the BBC the death of 14-year-old Hannah Smith of Leicestershire, a girl who suffered web bullying, was "absolutely tragic".
The prime minister said those running the websites had to "clean up their act", and if they did not, people should boycott them.
Hannah's father Dave said his daughter killed herself after being bullied on ask.fm. He has since called for tighter controls to be applied on social networking websites.
Ask.fm allows people to post comments anonymously. Hannah's father said he found posts telling her "to die".
The Latvia-based website said its moderators "ensure genuine concerns are acted upon immediately" and that it always removed "content reported to us that violates our terms of service".
In a statement, Ask.fm said: "We have reached out to Leicestershire police and would be happy to co-operate with their investigation into the circumstances.
"Ask.fm actively encourages our users and their parents to report any incidences of bullying, either by using the in-site reporting button, or via our contact page."
The latest controversy around social networking sites comes after police arrested three men from around the country, after alleged threats of rape and bombings were made against prominent women on Twitter.
The latest arrest was made in the Bristol area this week, and a police investigation is ongoing with other arrests possible.
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