Peter Chapman, a convicted sex offender, used Facebook to lure 17-year-old Ashleigh Hall to her death. Chapman, 33, set up a fake profile on the site – complete with stolen photographs – to pretend he was a boy of 19.

Yesterday, the Child Exploitation and Online Protection Centre (CEOP), which is responsible for tracking and prosecuting the country’s worst sex offenders, said Facebook had so far refused to introduce an official “alert button” with which youngsters could report suspicions that they were being “groomed” by online paedophiles or targeted by cyber-bullies.

The tool, developed by CEOP in 2006, is used by other networking websites including Bebo and MSN Messenger but Facebook has refused to incorporate it into its website. Jim Gamble, the CEOP chief executive, criticised the failure to include the alert button.

Of the 267 reports that the CEOP received about suspicious activity on Facebook last year, 43 per cent concerned grooming but “only one or two” came from Facebook itself, he said.

“The vast majority are coming from people who are, ironically, having to go to other sites that have our button and send the report to us. That is just not good enough,” Mr Gamble added.

Facebook insists its reporting system is good enough to handle reports of grooming, which are dealt with by staff who liaise with police. “We have reporting buttons on every page of our site and continue to invest heavily in creating the most robust reporting system to support our 400 million users,” said a spokeswoman.

But Mr Gamble insisted: “Their argument for not putting our button into their environment, in my opinion, doesn’t hold water. The button is a deterrent to offenders and provides users with a choice of either going to their social network provider or to CEOP for a range of advice and help.