Moped-riding thieves robbed a group of teenagers of a £1,600 bicycle and their iPhones in Carshalton.
Two robbers riding a silver and black moped approached a group of three 15-year-old boys and robbed them of the bike and their phones in Dale Park off Arlington Drive at about 8pm on Wednesday.
The bike is a highly specialised Enduro mountain racing bike and police want anyone who has seen it to get in touch as it is very distinctive.
One of the suspects is a black man, about 6ft tall and of stocky build. He was wearing a black crash helmet with a black visor. The second suspect is of mixed race Mediterranean appearance, about 5ft 7in and slim. He wore a silver or white crash helmet.
Detective Constable Steve Newman said: "These are good descriptions of the suspects and we believe they may live locally.
"Someone must know who they are, especially as it looks like they hang out together. If you do know their identity, please get in touch urgently before they are tempted to strike again."
If you have any information, you can call police on 101 or the charity Crimestoppers on 0800 555 111.