A 31-year-old man was cycling on the redway from Stacey Bushes towards Wolverton at 8pm on Wednesday, 14 March, when he came across a group of male youths near an underpass.
As he rode past the group, who were aged approximately 15 years old, one of them elbowed him causing him to fall off his bike.
The same boy then punched him in the face.
The victim then went to look for his bicycle in a nearby hedge but another boy from the group, who had a knife, then threatened him, and demanded that he hand over his possessions.
The victim said he did not have any belongings on him.
The offender who elbowed and punched the victim was white, small, of thin build and dressed all in black.
The second offender, who had a knife, was black and carrying a small bag. He was also dressed in black clothes.
The bicycle that the victim was forced to leave at the scene was a hybrid bike, and had 11 gears. It was black in colour, with white scratches down the metal near the front wheel.
Investigating officer Detective Constable Susan Russell said: “We would like to hear from anyone who witnessed the incident or has any information about the offenders to contact us.
“There was a second group of young people near the first and I would like to appeal to them to come forward if they saw what happened.
“Please call the Thames Valley Police non-emergency number on 101, quoting reference 43180078878, or alternatively Crimestoppers anonymously.”