Police were called at 7.44pm on Saturday, March 14 after a 14-year-old boy had been assaulted by a group of teenagers in Hinkler Green Park.
The group reportedly tried to steal the boy’s electric bike when the altercation occured, Hampshire Constabulary said.
The spokesperson added that some dog walkers intervened and the boy was able to get away, sustaining minor injuries.
Officers are now asking for the public’s help.
The spokesperson said: “Were you in the area at the time? Did you see or hear anything suspicious?
“If you have any information that may assist our investigation, or any relevant footage – mobile phone or CCTV – please call 101 and quote incident number 44260123141, or you can submit information by going to our website.
“You can also report any information 100 per cent anonymously by calling independent charity Crimestoppers on 0800 555 111, or by going to their website.”