This has been a challenge in several large cities like New York and Chicago in recent times. While law enforcement can monitor social media sites that are mainstream and public, there are so many social media outlets now that teens use and they are almost instantaneous and more difficult to follow for law enforcement.
Once a disturbance arises, it is also a serious challenge for law enforcement to respond with the appropriate amount of force. Often times the gathering of teenagers start peaceful and with no criminal intentions. But when things change they can escalate incredibly fast which leaves the police short of manpower to respond effectively, and caught in the balance how how to use force to protect the safety of people and property.