More children are struggling with feelings of loneliness and social media is being blamed.
Childline figures show that the NSPCC-supported service gave 4,636 counselling sessions that were devoted to loneliness in 2017-18.
This was a 14% increase on the previous year.
Most of those seeking help were teenagers but the youngest person was just 10 years old.
Some children said that comparing themselves to their friends and watching friends socialise without them made them feel isolated.
One teenage boy told Childline: "I see all my friends having a good time on social media and it gets me down, I feel like no one cares enough to invite me.
"My mood is getting worse and now I'm just upset all the time and can't stop crying."
Childline founder Dame Esther Rantzen said: "Loneliness needs to be taken seriously because it is potentially damaging to children's physical and mental health.
"The crucial question is: what is causing this rise among the young?
"Are we all too busy to make space and time for our children? Is it that we have lost the habit of eating together?
"Or is it the illusion created by social networks that everyone else is liked, popular and enjoying a far more exciting life so they feel lonelier than ever?
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"Whatever the reason, it's crucial that young people know they can always contact Childline to speak to someone who will listen and care about them."
The NSPCC's "Are you there?" campaign calls on the government to fund Childline so it can help more youngsters.
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