Facebook's apps are used for more than half of the UK's online grooming crimes, with thousands of offences across its social media sites since laws to clamp down on sexual communication with children were introduced four years ago.
Police are recording 24 online grooming crimes a week across Facebook, Instagram and WhatsApp, according to figures released to the UK children's charity NSPCC.
Some 18,436 offences under the Sexual Communication with a Child act were recorded between April 2017 and March 2021.
The means of communication was known in 9,660 cases. Of these, 5,120 used one of Facebook's three social media apps.
Facebook said it has introduced technology to combat online grooming and would continue to develop new ways to "prevent, detect and respond to abuse".
The figures come with Facebook whistleblower Frances Haugen to give evidence in the UK parliament tomorrow.
Haugen, who has accused the Silicon Valley firm of putting profit before Facebook users' safety, will answer questions for the Online Safety Bill committee.
British Prime Minister Boris Johnson has pledged criminal sanctions on tech giants responsible for allowing harmful content as part of the bill.
Facebook boss Mark Zuckerberg has previously said that Haugen's accusation "just doesn't reflect the company we know", adding: "We care deeply about issues like safety, well-being and mental health."
Sir Peter Wanless, NSPCC chief executive, said: "Frances Haugen's brave actions have shown the harm Facebook is causing children's mental health. The evidence we have gathered also reveals the extent to which their sites are being used by offenders to groom children.
"Instead of scribbling defensive blogs and setting their PR machine on journalists, Nick Clegg and Mark Zuckerberg must now publish all their research into how their platforms contribute to harm and sexual abuse and step up their efforts to fix their sites so they are safe for children.
"Meanwhile, Boris Johnson has a golden opportunity to change the global landscape with the Online Safety Bill if he turns the promises made this week into tough legislation."
A spokesman for Facebook said: "This is abhorrent behaviour and we work quickly to find it, remove it and report it to the relevant authorities. We also block adults from messaging under 18s they're not connected with and have introduced technology that makes it harder for potentially suspicious accounts to find young people.
"With tens of millions of people in the UK using our apps every day, we are determined to continue developing new ways to prevent, detect and respond to abuse."
Facebook will report its financial performance for the three months to September on Monday with pre-tax profit expected to be around £8 billion ($15.4 billion).
Facebook was last week named in legal papers filed with a New York court in a lawsuit pitting 15 US states and Puerto Rico against Google.
Papers claimed that Google "colluded" with Facebook to "kill" so-called header bidding – computer code that challenged the search engine's dominant position in online advertising.
Google is being sued over allegations that it used underhand tactics to gain its market position.
The court filings shed new light on Google's alleged dominance by comparing it to the financial markets.
They claim: "Imagine if the financial markets are controlled by one monopoly company, say Goldman Sachs, and that company then owns the NYSE, which is the largest financial exchange, that then trades on that exchange to advantage itself, eliminate competition, and charge a monopoly tax on billions of daily transactions.
"Obviously, no free, fair and functioning market could operate that way. Yet, that is today's world of online display advertising."
Kent Walker, Google's senior vice president of global affairs, attacked the case as "deeply flawed" when it was filed last year.
He said: "Google Search has put the world's information at the fingertips of over a billion people. Our engineers work to offer the best search engine possible, constantly improving and fine-tuning it.
"People use Google because they choose to, not because they're forced to, or because they can't find alternatives.
"This lawsuit would do nothing to help consumers. To the contrary, it would artificially prop up lower-quality search alternatives, raise phone prices, and make it harder for people to get the search services they want to use."