Police are warning of a new form of burglar called Facecrooks - gatecrashers who raid social-media arranged house parties and steal while the bash is going on.
Officers are talking to schools and parents about the new phenomenon which is increasing as term ends and the summer teen party season gets underway.
Concerns have also been raised about teenagers advertising they are planning to have a party on social media sites.
They said the thieves brazenly walk into the party when it is in full swing, and steal items from the house, and also rob people of their phones and wallets.
Parents of pupils at one school in Bristol, were warned of the phenomenon in an e-mail alert.
The message said: “The police have informed us that in recent months there have seen several teenage house parties in the area disrupted by gatecrashers who have been intent on stealing from the houses or robbing guests as they leave.
“If you are thinking of hosting a party for your child, or they are attending a house party, please be aware of this.”
While this specific warning was issued to parents in Bristol, the advice is relevant across the country and there have been some high profile examples of gatherings getting out of hand due to unwanted gatecrashers nationally.
In 2010, 15-year-old Rachel Ross ‘advertised’ a small party at her house on Facebook.
More than 50 people attended and caused around £15,000 worth of damage, including urinating on children’s beds.
Sarah Hine was just 14 when she invited up to 800 drunken youths to her mother’s home in Essex in 2012.
Approximately £30,000 worth of damage was caused, leading one neighbour to describe the scenes to the Daily Mail as ‘like Belfast in the 1970s’.
Back in 2008, £5,000 worth of damage was caused to Julia Anscomb’s house in Woking, Surrey after her 15-year-old daughter hosted a party there, which saw their five-month-old puppy Bailey fall ill after consuming unidentified pills.
In 2013, a house believed to be worth £1.1million in North London was trashed when a public schoolboy’s made a Facebook event .