Dean Hewitson of Workington, had his Kawasaki 250cc bike stolen from the garage behind his house last Thursday.
It was bolted on to a hydraulic pulley but thieves still managed to remove the black, four-stroke bike, which was not insured.
The 18-year-old, who has been riding since he was nine, said: “I feel totally gutted. This is the first bike I have bought for myself and I had a great year on it last season.
“I was the championship leader at the Fulton track near Lamplugh and I was looking forward to having another good season.
“I can’t believe someone would steal my bike. I have worked so hard to try to make a name for myself.”
Dean had just secured £1,500 worth of sponsorship from his employer Gates Tyres to help him get through the new season.
The new motocross season begins again in March but Dean isn’t sure he’ll be on the starting grid as he cannot afford a new bike.
He added: “Bikes are really expensive and my family don’t have the money to buy a new one.
“I don’t know what I’ll do if I can’t ride this season. Right now I’m just hoping the police are able to find my bike.”
His mum Sharon said: “Dean is a great lad and has done so well. This has been a major blow for him and I’m hurting for him.
“I know his bike is out there somewhere, we just pray that whoever has taken it will return it so Dean can continue to do what he loves.”
Anyone with any information is asked to contact police on +448453300247