Amplified, a joint scheme formed by organisations including The Prince's Trust, Scouts, UK Youth, Redthread and StreetDoctors, is offering activities from kayaking to dance.
It is also intended to provide safe spaces, promote positive role models, and draw advice from those who have experienced violence.
Amplified campaigner Omar Sharif, who has been affected by gang crime and now works to inspire young people to break away from such influences, said: "If young people share our experiences and the things we've been through, we can have a powerful impact on other young people whose lives are at risk of taking a negative turn.
"Even if I change just one person's life for the better it will be worth it, but I believe long-lasting change will be made by giving young people role models who are relatable and who direct them to the services and support they need."
Research by The Prince's Trust found that 66 per cent of young people in the UK think having positive role models would help to reduce violent crime among young people, while 45 per cent believe there are not enough alternative activities for young people.
Recent government data shows that there has been a 77 per cent rise in knife-related homicides by under-18s between 2016 and 2018, and a 93 per cent increase in the number of under-16s admitted to hospital due to knife attacks since 2012.
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Ian Jeffers, deputy chief executive of The Prince's Trust, said: "Violence levels in this country have reached staggering highs and we need to do everything we can to protect our young people and give them an alternative life.
"Our Amplified initiative will see the youth sector promoting positive role models and free activities to those who need them most.
"Together, we have the commitment, scale and influence to make a real difference to young people in this country."
Maddie Dinwoodie, deputy chief executive of UK Youth, added: "We know that a major contributing factor to serious youth violence is local deprivation; often characterised by young people not having access to activities in their communities.
"In disadvantaged areas local funding cuts and austerity have made the issue worse, meaning that the young people who most need these activities cannot access them.
"By supporting the Amplified campaign we want to make the link between engaging young people in opportunities and reducing serious violence."
The Scout Association said: "We are so proud to be supporting such brilliant work with the Princes Trust and other great organisations, promoting opportunities, skills and positive futures for young people."