A teenage boy was threatened in a play area by a robber claiming to have a knife.
The 16-year-old was with friends at the play area on Southampton Common when he was confronted by an older youth.
He demanded the 16-year-old hand over his mobile phone, telling him he had a knife.
The offender then tried to steal the victim's bike, but he managed to get it back straight away.
The attacker then pulled something from his pocket, but it was not clear whether or not it was in fact a knife.
The offender - who left empty handed - is described as white, 17-years-old, 6ft 4ins tall and of a thin build with a slim face and fair eyebrows.
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He was wearing a black waist length jacket with the hood up, dark blue jeans and grey fleece gloves.
Investigating Officer PC Bowman said: "I urge anyone who thinks they may recognise the e-fit and the description of the offender to the contact police.
"The young offender is particularly distinguishable because he is very tall and slim."
The incident happened on Tuesday, January 22 around 3.45pm, but details have only just been released.
If anyone witnessed the incident, or recognises the e-fit or descriptions, they should contact PC Bowman at Portswood police station on 0845 045 4545, or call Crimestoppers anonymously on 0800 555 111.
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