The website linked to the suicide of British teenager Hannah Smith, as well as two Irish girls, is facing a backlash after several major companies decided to withdraw advertising from the site.

Specsavers, Vodafone, Laura Ashley and charity Save the Children have all pulled ads from ask.fm.

Hannah, 14, was found hanged on Friday after being bullied on the website.

The suicides of 15-year-old Ciara Pugsley in Co Leitrim and 13-year-old Erin Gallagher in Co Donegal have also been linked to comments on the website.

A Specsavers spokesman said the company had instructed ask.fm to remove all of its adverts from the site due to "deep concerns over cyber-bullying".

Save the Children added: "We put the welfare of children first and as a result of the tragic case of Hannah Smith we no longer advertise on ask.fm."

Earlier, British Prime Minister David Cameron said internet users should boycott "vile" websites which allow cyber-bullying to avoid more deaths of young people who receive abuse online.

Mr Cameron said website operators must "step up to the plate" to ensure users are protected.

Hannah's father, David Smith, said those who run the website should face murder or manslaughter charges and

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Speaking during a visit to a hospital in Salford, Mr Cameron told Sky News: "The people that operate these websites have got to step up to the plate and show some responsibility in the way that they run these websites.

"Just because someone does something online, it doesn't mean they're above the law. If you incite someone to do harm, if you incite violence, that is breaking the law, whether that is online or offline.

"Also, there's something all of us can do as parents and as users of the internet and that is not to use some of these vile sites. Boycott them, don't go there, don't join them - we need to do that as well.

"I'm very keen we look at all the action we can take to try and stop future tragedies like this."

Ask.fm described Hannah's death as a "true tragedy" and promised to work with police investigating the incident.

The question-and-answer site allows users to send messages to one another without their identity being disclosed.

Although users have to register an email address, name and date of birth, those posting messages can do so anonymously.

A spokeswoman for the website said: "Hannah Smith's death is a true tragedy. We would like to convey our deepest condolences to her family and friends.

"We have reached out to the Leicestershire police and would be happy to co-operate with their investigation into the true circumstances of her suicide.

"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.

"All reports are read by our team of moderators to ensure that genuine concerns are heard and acted upon immediately - and we always remove content reported to us that violates our terms of service."

Hannah, from Lutterworth, Leicestershire, was found by her sister Joanne, 16.

Mr Smith said he was driving his lorry when Joanne called him to break the news.

"I was 50 miles away in a lorry and I got a phone call from Joanne to say Hannah has hung herself," he told Mirror Online.

"And then Joanne put the phone down on me and I had to ring back to find out what was happening because I didn't have the faintest idea what was happening.

"And then I spoke to my brother and my brother turned round to me and he said 'Hannah's hung herself'. And I said 'Is she dead?' and he said 'Yes' and I just broke down.

"I turned the lorry round as fast as I could to get back."

Mr Smith, 45, found the ask.fm messages the morning after Hannah died.

"There's something not right with the world today if people can tell somebody to die so many times that they actually do it," he said.

"Me, personally, I think ask.fm - the people that run it - should get done for manslaughter or murder because you try contacting them and they just don't care. They don't care that teenagers are dying and killing themselves. It can't be right.

"These websites should be got rid of. If nothing else, they need to be regulated."

Hannah's older sister Joanne told the Daily Mirror she was being subjected to the same hateful taunts as her sister, while a Facebook page dedicated to Hannah had also been targeted.

Leicestershire police confirmed it had been contacted by Hannah's father David about further claims of "inappropriate postings" on Facebook.

"I've just lost my sister and now I've got to deal with getting abuse myself," Joanne told the paper.

"These trolls don't care what happened to Hannah or what we're going through, they just live in their sad little worlds.

"It's really upsetting. I'm struggling to cope with what's happened and don't need these trolls hounding me."

A spokeswoman for Leicestershire police said: "Mr Smith, Hannah's father, has contacted police regarding inappropriate postings on a Facebook page. They are being considered as part of an ongoing investigation."

Facebook confirmed that it had received reports of inappropriate comments posted to a tribute page to Hannah Smith and any which violated the website's terms have been removed.

Companies often buy their advertising through agencies.

They can buy "bundles" of advertising that mean their brands appear on several sites - so sometimes they are unaware of where their adverts are displayed.

For instance, mental health charity Mind only found out today that ask.fm carried their adverts.

A spokeswoman said: "We were unaware that the ask.fm website carried adverts for Mind and Time to Change until Radio 4 contacted us at lunchtime today.

"Our advertising on this site forms part of packages arranged for us by agencies, and we are this afternoon in the process of pulling all advertising from this site."

The Sun newspaper has also instructed the agency handling its advertising to "blacklist" the outlet - meaning no more adverts from the newspaper should appear on the site.