Facebook’s plans to become more privacy-focused could put children at risk of abuse, with encrypted communications meaning abusers could work in secret.
Peter Wanless, chief executive of the NSPCC - said end-to-end encryption on Facebook Messenger was a ‘risk and a backward step’.
The social media giant pledged to begin a 'new chapter' in its history as it revealed plans to be more privacy-focused at its annual developer conference in California in April.
In an interview with The Daily Telegraph, Mr Wanless said: 'It places privacy and secrecy ahead of accountability and transparency.
'It's really disappointing that reaction to the NSPCC's call for a safer internet is to make it more secret and more dangerous.
'What I would say to Mark Zuckerberg is: you have a duty of care and a responsibility to the people who are using your services, very many of whom are children and young people.'
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Mr Wanless said social media firms should be proportionately punished for breaches of child safety given they 'make vast sums of money every year', adding that their directors should be held liable.
The firms were not disclosing the extent of child abuse on their platforms, Mr Wanless said, citing NSPCC research which showed 20% of primary school children had been asked to undress while livestreaming.
'Companies are a black box. Many of them don't publish or tell you about the scale and the scope of the dangers,' he said.
Facebook's vice-president of global affairs and communications, Nick Clegg, told the Financial Times that the company had 'made mistakes but has taken responsibility and is addressing them'.