Police have launched an investigation following the incident in Scawthorpe yesterday.
And the latest probe comes just hours after a group of teenagers were robbed by a balaclava clad gang wielding a knife in another shocking Doncaster incident.
They are are not believed to be connected.
A brief statement said: “It is reported that at around 5pm yesterday, a 12-year-old boy and his friend had been threatened by a group of teenagers with a knife on Jossey Lane, Scawthorpe.
“They demanded the victim hand over his bike, but fled the scene empty handed.”
Anyone with information which could help the investigation should call 101 quoting incident number 712 of 15 March.