Police are appealing for witnesses following the robbery, which occurred in Earlsheaton Park in Dewsbury on Friday 31st May 2019.
PC Tom Howell of the Batley and Spen Neighbourhood Policing Team is investigating the incident and said:
“This was an upsetting ordeal for the teenager who was subject to kicking and punching from the group.
“They also tried to take his mobile phone during the incident, but made away with £13 cash.
“We know that a dog walker shouted at the group as the incident unfolded and we are calling for any witnesses or anyone with information about those responsible to come forward.
“This is unacceptable behaviour and if you can help in our enquiries, please call the non- emergency number 101 or Crimestoppers in confidence on 0800 555 111.
“Alternatively, you can use the Online Live Chat system accessible via the Force website.”