Teenagers in Philadelphia playing basketball
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Curfew for flash mobbing teenagers in Philadelphia

Authorities in Philadelphia have instructed a weekend curfew for under 18 year olds, to try to stop teenagers from wreaking havoc due to flash mobbing.

Flash mobbing, where groups gather after communicating through social media and rampage through the town centre, is frightening residents and alarming Philadelphia's city government.

Crowds of teenagers have beaten and robbed people, and shops have been damaged.