The youngster was not hurt in the incident, although he was badly shaken up.
But it was the third serious incident on Lord Street in less than a week, following police investigations into separate allegations of rape and robbery on the same street.
It comes after a recent public meeting was held in the town to highlight concerns about crime and policing in the area.
The bike robbery occurred is reported to have occurred between 6.30pm and 7pm last week, on Thursday, October 28. As the youngster was cycling on Lord Street, close to Iceland supermarket, he was approached by two men.
One of the offenders threatened the boy with a knife, taking the bike, a dark grey Carrera with orange trims.
The offenders then quickly left the scene, at the junction with London Street, and made their way towards Dock Street.
Police said: “We are appealing for information and urging any witnesses to come forward.
“If you can help in any way, please get in touch.”
No arrests had been made by Monday afternoon.
Anyone with information can phone 101 or email [email protected] quoting log 1445 of October 28.
Fleetwood Coun Brian Crawford said: “This serious crime spike is very worrying but police have been told of people’s genuine concerns.”
Coun Crawford added: “I have met up with Andrew Snowden, the Police and Crime Commissioner for Lancashire, and he is looking to spend up to a billion pounds to tackle crime in
Lancashire and hold the police to account.
“He is very aware of what is happening in Fleetwood and so is the Chief Constable.”
Some residents say the rising crime levels are due to an influx of people from outside Fleetwood coming to live in the town, while others say cutbacks to police and high levels of unemployment and deprivation are factors.
Many residents voiced concerns on Fleetwood Area Police Facebook site.
Another public meeting about crime is at the Strawberry Gardens Pub on Saturday November 20 at 4.30pm.