Advertisers have severed ties with chat website Ask.fm in the wake of the death of teenager Hannah Smith who was found dead after she was abused on the site.
Vodafone, Save the Children and Specsavers were the first companies to pull their advertising from the social media platform over concerns about online bullying.
The Sun newspaper, eBay, BT and EDF were among the comapnies who later announced they were also dropping their adverts from the website.
Prime Minister David Cameron urged social media sites to "step up to the plate" and deal with how they intend to tackle online abuse following the death of the 14-year-old.
Hannah was found hanged at her home in Lutterworth, Leicestershire, after frequently receiving abusive messages on Ask.fm. The website allows users to ask questions and send messages to each other anonymously.
A post mortem into her death was inconclusive.
Specsavers has removed all advertising on the site due to "deep concerns over cyberbullying".
A spokesperson for the charity 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."
Cameron said the government was looking at how to protect people from being abused online and called for a boycott of sites that appear to not tackle the problem.
He said: "It's not the case that there's nothing we can do just because it's online. There are some steps that need to be taken.
"The people that run these websites have got to step up to the plate, clean up their act and show some responsibility.
"It's not acceptable what's allowed to happen on these sites. It's their responsibility, and those posting these hateful remarks, first and foremost.
"Just because something is done online doesn't mean that it's legal. If you incite hatred, if you incite violence, that's a crime, whether you do it in a television studio, on a soapbox or online. So these people can be chased.
"If websites don't clean up their act and don't sort themselves out then we as members of the general public have got to stop using these particular sites and boycott them."
Never happen again
Campaign group BeatBullying is also calling for people to boycott the site and for adverisers to continue leaving the site in protest of Hannah's death.
The group said: "Ask.fm needs to take its users' safety much more seriously, which includes putting adequate resources behind its safeguarding policies.
"For some young people, this site has become an ecosystem of hate and we must ensure that cases like Hannah's can never happen again.
"Until this happens, we're calling on the public, young people, parents and schools to boycott Ask.fm.
"We're also urging advertisers whose funding provides the lifeblood of the site to think very carefully about their advertising spend on this platform."
The founders of Ask.fm, Mark and Ilja Terebin, published an open letter in response to the criticism.It said: "We would like to reassure all users and parents of users that we are committed to ensuring that our site is a safe environment.
"We do not condone bullying of any kind, or any form of unacceptable use of our site.
"We have implemented various measures over the past months to continue to improve our users' safety, and we have implemented improved reporting policies."
It continued: "The vast majority of our users are very happy teenagers, who use Ask.fm to converse with their peers around the world about the things that interest them.
"Bullying is an age-old problem that we in no way condone - and while its evolution online is disturbing, it certainly is not unique to our site.
"We will continue to work with the appropriate organisations to safeguard against bullying on Ask.fm - and we would welcome the opportunity to align with the rest of industry and society in fighting it on a higher level."