Is there a solution? A new survey for the BBC asked 2,000 teenagers about their biggest worries and hopes. Many fear their concerns will not be addressed.
Knife crime, online safety and mental health
Teenagers: Not recognised as a group until about 100 years ago, teenagers have serious concerns and have led major political protests in recent years. Glossary
Irrational - Not thought through or nonsensical.
Impulsive - Acting without thinking much about it.
Apathetic - Showing no interest.
Incentive - Something that motivates you to do something. A reason.