NEW YORK - Teenage gangs are being linked to about 40 percent of the city's shootings. 

According to police, there are more than 300 violent crews of 12- to 20-year-olds in New York City. 

Experts say the trend of smaller, younger gangs has been on the rise over the last few years as authorities have cracked down on bigger, more traditional gangs. 

The gangs are clustered around a particular block or housing project. Authorities say much of the violence stems from arguments on social media.