Facebook party invite leads to riot
22 September 2012 Last updated at 16:43 BST
In the Netherlands, riot police were called in to contain the situation when thousands of youths descended on the northern town of Haren after an online invitation to a girl's 16th birthday party went viral.
The girl and her family had to leave their home as thousands of young people turned up in response to a message she had posted without marking it as a private event.
More than 20 people were arrested and three people were seriously hurt.
Anna Holligan reports.