65871, PALO ALTO, CALIFORNIA - Saturday August 27, 2011. **EXCLUSIVE** Facebook CEO Mark Zuckerberg takes his dog Beast for a walk with a female friend believed to be his Chinese teacher. The young entrepreneur, who was recently estimated to be worth $13.5 billion, originally set out to learn Chinese to prepare for a trip to China with his girlfriend Priscilla Chan. Photograph: Bruja, ?