The campaign was created by a group of nine young people who have felt lonely in the past, in partnership with specialist youth co-design agency Effervescent, and the Co-op Foundation.
Research has revealed only 26 per cent of young people are confident talking about loneliness, and even fewer (23 per cent) believe society treats it as a serious social issue.
Yellow socks were chosen as the campaign idea because the colour reminded the young people of hope, while the semi-hidden nature of socks reflected what loneliness felt like for them.
Taylor, 13, from Greater Manchester, helped create the campaign. She said: "This project has really developed my confidence. I have realised through this process that I am loveable and wonderful after all, and that has helped me to find deeper and better friendships at school."
The young people also helped create characters for an animation that reflected how lonely they felt. Characters include a unicorn and a ‘crocoduck’ - a duck that pretends to be a crocodile to fit in with others. The animation is narrated by 15-year-old Mia Povey from Middlesbrough.
People are invited to get involved whenever and wherever they like. Every time someone wears yellow socks, they’ll show young people everywhere that youth loneliness matters.
Supporters can then post a picture of themselves online using #LonelyNotAlone.
Jim Cooke, head of the Co-op Foundation, said: "Loneliness is a feeling we can all relate to, but few of us realise that young people are affected more than any other age group. Get involved today to help young people everywhere see that youth loneliness matters and that even if they do feel lonely, they are not alone."
Culture secretary Nicky Morgan added: "I hope this campaign will encourage more people to spot the signs of loneliness, speak up and build more meaningful connections with each other."