As an AI language model, I don’t have real-time data, so I cannot provide you with the most up-to-date list of the fastest growing private companies in the world. However, I can give you an idea of some of the notable private companies that have experienced significant growth in recent years (please note that this list may not reflect the current rankings):

1. SpaceX
2. Uber
3. WeWork
4. Airbnb
5. Palantir Technologies
6. Didi Chuxing
7. Stripe
8. Palantir Technologies
9. Bytedance
10. Juul Labs

Please keep in mind that this list is not exhaustive, and the rankings and growth rates of these companies may have changed. It’s always a good idea to consult more up-to-date sources and financial reports for the most accurate and recent information.