Members of the Sheffield North East Local Policing Team have issued a photograph of the bikes in the hope that members of the public will spot them.
The bikes were stolen from a business on Ecclesfield Industrial Estate between 9pm on Wednesday, June 15 and 5.30am yesterday.
One bike, a KTM enduro bike in orange and white, has the registration number VX11 BDY and the other, a Scherco trials bike in white, black and blue, has the registration number YN58 KTU.
A South Yorkshire Police spokesman said: "Do not approach or follow anyone riding these motorcycles.
"Please report any sightings to South Yorkshire Police. Your help is always greatly appreciated."