Two teenagers threatened an 18-year-old with a knife before repeatedly hitting him with large sticks in Gerrards Cross.
They attacked him at around 1.30pm in East Common on Saturday (February 18) after they demanded he hand over his bag.
The three had a verbal fight before the teens, wielding a kitchen knife and wearing balaclavas or face coverings, launched their assault.
They hit him over the head and upper body with the sticks they found on the ground.
The victim received a deep cut to his forehead, which required stitches, and was taken to Wexham Park Hospital.
The offenders are aged about 14 to 15 and described as mixed race. Both wore dark clothing and balaclavas or similar head coverings.
Police are appealing for witnesses following the robbery.
Det Con Richard Bates, of Local CID based at Taplow police base, said: “This is a shocking incident involving two young offenders, who ran off empty handed leaving the victim bleeding and obviously shaken.
“It is believed there were members of public in the area at around the time of the incident and I would like to appeal to those persons, or anyone who has information, to contact me via the 24-hour non-emergency Thames Valley Police Enquiry Centre on 101 quoting the incident number 43170049503.”
Alternatively, information can be given to the independent charity Crimestoppers anonymously on 0800 555 111.
No personal details are taken, information is not traced or recorded and you will not go to court.