Ask.fm, the website linked to the suicide of teenager Hannah Smith, is facing a backlash after several major companies decided to withdraw advertising from the site.
Specsavers, Vodafone, Laura Ashley and charities Save the Children and Mind have all pulled ads from Ask.fm. The Sun has also requested an advertising "blacklist" of the site so its ads no longer appear.
Hannah, 14, was found hanged on Friday after being bullied 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, the Prime Minister said internet users should boycott "vile" websites which allow cyber-bullying to avoid more deaths of young people who receive abuse online.
David 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 called for more regulation of social networking sites.
Hannah's sister and father, Jo and David Smith
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, 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."
Facebook also 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.