Police have questioned almost 2,000 children, some as young as nine, with regards to online bullying and abuse on social media.

The figures reveal more than 1,200 children under the age of 18 have been cautioned or given warnings or fines as a result of online "trolling".

The figures, based on Freedom of Information (FoI) requests by Sky News, also showed almost 20,000 adults have also been investigated by police for similar offences over the past three years – a rate of around 20 cases a day.

Sky News added the true figures may be much higher, as 18 police forces in the UK failed to provide data following the FoI request.

Luke Roberts, a social network expert at Beat Bullying, told Sky News: "There are more devices than ever. So whether it's smartphones, internet-connected TVs, more apps - they allow more young people to be harassed than ever before.

"In terms of social networking, we'd like to see more transparency, in terms of giving clear reporting mechanisms to children."

The investigation looked to reveal the number of cases police had investigated under Section 127 of the 2003 Communications Act.

The law was enacted following a number of high-profile cases involving social media abuse. The legislation also covers abuse via text messaging and phone calls.

The figures show over a three year period, 1,932 children were investigated under the online harassment laws and 1,203 were either charged with a criminal offence, fined, cautioned or given a verbal warning.

Four 10-year-olds and one nine-year-old were given warnings by police in Tayside for their online behaviour.

Overall, the Metropolitan Police have charged the most adults and children in connection with online bullying and harassment out of all the forces with 2,099 cases.

Hertfordshire Police recorded the highest number of cases last year with 1,042 - up from 291 in 2011.

In total, 19,279 adults have been investigated over the last three years, with 11,292 having some sort of police action taken against them.

Ellie, a teenage victim of online harassment who reported her case to police after receiving death threats, described the figures as "shocking".

"They stalked me and knew a lot about me," she said.

"I drove at the time and where I used to live there's a little bridge. And within hours of driving over it, there was a comment saying you should have crashed your car over the bridge you drove over.

"With bullying that happens at school, people can get away from it at home. For me, this literally followed me everywhere I went."