A Kiwi teen mountain biking sensation's Junior World Series title hopes are in jeopardy after her bike was stolen overnight.

Jessica Manchester, 16, has earned a place in Junior World Series but her dreams could now be left in tatters after, according to her sister Jemma, Jessica's bike was stolen before her race in Austria on Monday.

A Givealittle page has been set up to raise money to help fund a new bike for Jessica.

"As Jessica's sister, supporter, training partner and best friend, I have personally seen Jess give it her all this year to get here, but unfortunately her bike hasn't yet been found," the Givealittle page said.

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"This bike is really important to Jess and has a lot of memories and meaning. I am starting this fundraising page to help get #justiceforjess.

"This fundraiser is to help Jess in any way she needs to get a bike to race for the following junior world series coming up ahead of her," explained her sister.

Despite the theft, Jessica pulled off an incredible third placing at Orbertraun in Austria while racing on an unfamiliar bike.

So far $2085 has been raised in less than 24 hours.

The 16-year-old has an impressive haul of titles including U15 NZ champion, two-time U17 NZ champion and two-time U17 Oceania champion in 2014 and 2015.