LOS ANGELES , California ( CNN ) -- A one-of-a-kind bicycle belonging to U.S. cycling legend Lance Armstrong was stolen from a team truck in California just hours after he rode it Saturday on the first day of a nine-day race . Lance Armstrong 's bike was stolen after he competed in the first day of the Amgen Tour of California . Cancer survivor and seven-time Tour de France champion Armstrong is racing in the Amgen Tour of California this week as he attempts another comeback after retiring from the sport in 2005 . Armstrong 's first comeback came in 1998 , two years after he was diagnosed with advanced testicular cancer that had spread to his lungs and brain . Doctors gave him a less than 50 percent chance of survival . Armstrong announced the bike theft on his Twitter account Sunday morning and posted a photograph . `` There is only one like it in the world therefore hard to pawn it off . Reward being offered , '' he wrote . The bicycle that was stolen is not the one Armstrong rides every day during the race . The stolen bike is used only for time trials , a race in which cyclists ride individually at staggered intervals over a set distance and try to get the best time . The thieves took four bicycles from a truck Armstrong 's Astana team had parked behind a hotel in Sacramento . The other three bicycles belonged to team members Janez Brajkovic , Steve Morabito and Yaroslav Popovych , Astana said . Armstrong , 37 , won the Tour de France , considered the premier bicycle race in the world , a record seven times from 1999-2005 . The 750-mile Amgen Tour of California ends Sunday . It is the second major race in which Armstrong has participated since announcing his comeback in September . He raced last month in the Tour Down Under in Australia , finishing 29th . Armstrong said he is aiming for another Tour de France victory this summer and was not expected to contend in the Australian race , which he used to gauge his fitness level after more than three years out of the saddle .
One-of-a-kind bicycle taken from team truck in California . Armstrong posted announcement of theft on Twitter account . Champion cyclist aiming for comeback with participation in Amgen Tour .