The incident took place near Abbeydale Road South at 4.45pm on Friday, 10 July. The man was riding his bike away from the city centre when he saw a white Ford Transit van reverse into the Abbeydale Industrial Hamlet.
As the victim approached the Hamlet, a man got out of the van and punched him before stealing the bike. The van was then driven away towards Dore and Totley railway station.
The victim was not seriously injured. The stolen bike is an electric Voodoo Zobop E bike in bright green and black.
The van came from the direction of Abbey Lane and it is reported there were three men inside, including the driver. An orange item was also placed in the front windscreen.
Anybody with information should call 101, quoting incident number 629 of 10 July.