Teenagers who contribute a self-portrait photograph with the message “I say no to knives” will be the stars of a new £3m Government campaign.

Largely-blank posters appearing in knife-crime hotspots will be gradually updated with images of supporters.

Young people can back the campaign and submit their image by visiting the “It Doesn’t Have to Happen” page on the Bebo social networking website.

The posters will be put up in dozens of areas including Manchester, London, Birmingham, Nottingham, Swansea, Portsmouth and Slough.

Home Secretary Jacqui Smith said the move is part of a £3m marketing campaign aimed at deterring youngsters from arming themselves with knives.

She said: “I want young people to stand united with us in the fight to tackle knife crime and send a clear message that weapons won’t be tolerated on our streets.

”Over 60,000 young people have visited the ‘It Doesn’t Have to Happen’ page on Bebo and the site has over 6,000 friends.

”The vast majority of young people are honest and law-abiding and it is crucial that we all spread the message more widely that carrying a knife is not acceptable. We can’t do this alone - we need the help of local communities to make a stand.”