A man was punched and kicked in the head and robbed of his mobile phone as he walked alongside Milton Keynes library.
The attack happened around 5pm on Wednesday (September 12), near the footbridge leading to Coltsfoot Place in Conniburrow.
The victim, aged 19, sustained injuries to his head and face including swelling to his eye and a cut lip.
The youths ran off across the bridge towards North 9th and North 10th Street.
Investigating officer PC Steve King of the Investigation Hub based at Milton Keynes police station said: “There were a lot of people in the area at the time of this offence and we are trying to identify witnesses who may have seen the offenders or the incident.
“I am urging anybody with any information to call 101 quoting reference number 43180279620, or call Crimestoppers anonymously on 0800 555 111.
“Alternatively, you can visit https://www.thamesvalley.police.uk/tua/tell-us-about/cor/tell-us-about-existing-case-report/ and provide all the details there.”