More than 400 children have been identified as victims of abuse over the past year by the UK's national centre for child protection.
The Child Exploitation and Online Protection centre (Ceop) said the children had been safeguarded or protected as a result.
And it said more than 500 people had been arrested for child sex offences.
But the "great tragedy" is that much child abuse goes unreported, said its chief executive Peter Davies.
Ceop was set up in 2006 to track online paedophiles and bring them to court.
In its annual report, the centre said 414 children were helped, 513 people arrested and 132 offender networks broken up in the UK in the past year. This is a record number of children and a record number of arrests for the centre.
Over a five-year period the agency said it helped to dismantle more than 394 high-risk sex offender networks and arrest 1,644 suspected paedophiles.
'Suffering in silence'
According to the report, images on the internet appear to show that younger children are increasingly becoming victims of abuse.
Mr Davies told the BBC: "The great tragedy and the great challenge for us is that so much child abuse goes unreported.
One of the unique things we do is use the internet to identify people who pose a risk to children and identify children who are at risk who otherwise would have just carried on suffering in silence.
"There is far more child abuse going on out there than ever gets reported. It's a major concern, it's something everyone needs to pull together and do something about."
He added: "Our contribution to that is to highlight it and do what we can using our technical expertise and our partnerships to stamp out the offending.
"And make sure that children and young people, and their parents and whoever cares for them, have the best possible advice and guidance so that they can empower themselves."
Mr Davies said Ceop was trying to stay ahead of developments in technology, including in the area of social networking sites.