The figure has come from the NSPCC at the start of Anti-Bullying Week.
The number of children and young people tormented at the hands of online trolls has increased by 88% in five years.
The figure has come from the NSPCC as the charity publishes its latest report 'What children are telling us about bullying'.
The worrying figures, released at the start of Anti-Bullying Week, show the charity's helpline service, Childline counselled 4,541 children about online bullying in 2015/16 compared to 2,410 in 2011/12.
In a quarter of counselling sessions children and young people were also counselled for a mental health and wellbeing issue, including low self-esteem, self-harm, suicidal thoughts and depression.
Children as young as 7 told Childline counsellors how they were being tormented and abused by malicious and hurtful messages from which they felt there was no escape.
The comments posted on their social media profiles, blogs and online pictures ranged from bullying and abusive words about how a young person looked to death threats and in the most extreme cases directly telling them to go and kill themselves.
One girl reported to Childline: "Every day I wake up scared to go to school, scared about the comments people will make and scared about walking home. Then I get in and log onto my social networking site and there are horrible messages everywhere. It's like there is no escaping the bullies. I'm struggling to cope with how upset I feel so sometimes I cut myself just to have a release but it's not enough. I can't go on like this."
And another young person who contacted Childline said: "It might sound like not much of a problem but there's a group of people I play with online and they told me to kill myself. I won't kill myself but it upsets me. My parents don't realise how upset it's making me and they tell me to stand up for myself or just not play anymore but they don't know how hard that is! I don't know why they have suddenly started picking on me but it hurts so much."
The advice given by children and young people on dealing with bullying includes:
* Tell an adult you can trust
* Keep a diary of what the bullies do including dates and descriptions
* Write a letter to your Headteacher
* Don't react, show the bullies you don't care and they will often lose interest
Children and young people can contact Childline for free, confidential support and advice, 24 hours a day on 0800 1111 or at www.childline.org.uk.