John Caudwell, Britain's seventh richest man, had his £5,000 bike stolen while at an Olympic torchbearers' reception at City Hall on Friday night.
Self-made billionaire Caudwell, 51, chained his bike to a stand outside City Hall before going inside to meet the mayor and fellow Olympic torchbearers.
Mr Caudwell said: "Ken had been talking about the Olympic spirit and how uplifting and wondrous it is for mankind.
"I come out and find my bike's gone."
The billionaire businessman, who set up and owns Phones 4U, is in training for a 2,300 mile charity bike ride from Athens to London.
He has now offered a £500 reward for the bike's return, and added: "I am horrified by the state of law and order and I'm a great advocate of change in the way law and order is conducted and an advocate of much tougher sentences."
Caudwell is a keen cyclist and regularly rides the 160 miles from the Phones 4U head office to London for business meetings.
The bike, a carbon fibre and titanium cycle, was bought four years ago for £5,000, and Mr Caudwell has done 30,000 miles on it.
He is now trying to organise an urgent replacement from the bike's manufacturers to train for the 18-day fundraising ride after the Olympics.
The Caudwell Charitable Trust has raised millions for children's charities in the UK.