The boy was allegedly pushed against the sea wall by the man near West Park.
The States police say the boy was uninjured but left shaken.
The man is believed to be aged in his 50s and is about 5ft 8in tall, with grey hair. He was wearing a grey T-shirt and dark shorts.
In a statement, the States police said: ‘The man… allegedly pushed the teenager against the sea wall and held him there for a short time. The man then jogged off in the direction of St Aubin. It is believed that he may have been responding to actions by the teenager.’
Anyone with information is being asked to phone the States police on 612612 or Crimestoppers on 0800 555 111.
