A 15-year-old boy was robbed by a group of six youths in Lewknor.
The youngster was walking his dog in the Community Park when the group approached him and demanded that he emptied pockets. They then stole his keys.
The youths were all white and wearing hooded tops.
PC Mark Riding, investigating the incident, said: "This is an area that is very rural and we think local people may have information about these youths.
"The young boy targeted has been left shaken up and we are hoping that we can clear this incident up quickly."
Anyone with any information about the incident, which happened on Sunday, to contact PC Riding at Thame police station via 0845 8 505 505, or if you do not want to talk to the police or give your name, call the Crimestoppers charity on 0800 555 111.
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