A gang robbed a cyclist near Sandford Lock on Saturday.
Police are appealing for witnesses after an 18-year-old man was robbed while cycling across the meadow by the River Thames between Kennington Railway Bridge and Sandford Lock, Sandford-on-Thames, at 5.45pm.
A gang of six teenagers - three on motorbikes - approached the teenager and threatened him.
They forced him to hand over his mobile phone and cigarette lighter.
The robbers were all male, aged between 16 and 17, and were wearing tracksuit bottoms and hooded tops.
All were wearing helmets, apart from one, who is between 5ft 8in and 5ft 9in tall, slim, with shaved, cropped blond hair.
Pc Tony Lee, based at Abingdon police station said: "I appeal to anyone who may have been walking along the River Thames between Sandford Lock and Iffley on Saturday and saw six youths of these descriptions to contact police immediately.
"The motorbikes are described as Pit Field' bikes, which were black-and-white, blue-and-white and yellow-and-red in colour.
"This type of behaviour will not be tolerated and I appeal to anyone who may be able to help our investigation to get in touch."
Anyone with information should call police on 08458 505505 or speak anonymously to Crimestoppers on 0800 555111.
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