Detectives are searching for three juveniles after a teenage boy was allegedly punched in the face and robbed of his e-bike in Beckenham Saturday morning.

Police say the incident unfolded about 9.45am at the Kenwick Link/Ladywell Street underpass.

The victim was approached by a group of three young people before one of them struck him in the face, pushing him off his e-bike.

The group, described by police as being aged between 13 and 15 years old, then fled the scene with the allegedly stolen e-bike.

All three were wearing black puffer jackets at the time of the incident.

Cannington detectives are investigating the aggravated robbery and are appealing for anyone with information to come forward.

Anyone with information in relation to this incident to contact Crime Stoppers at www.crimestopperswa.com.au or by calling 1800 333 000.

Dash cam, mobile phone or CCTV footage can be uploaded directly to investigators via this link.