With the pervasiveness of Facebook, Twitter and YouTube in our internet driven lives, it's hard to imagine a country where half a billion internet users don't have access to these and other websites we take for granted--but it's true. China has the largest internet population in the world but thing work a bit differently there, not least because of the 2 million people employed by the state to monitor web activity.
This can be especially challenging for expats and people staying connected with family on the other side of the border. Even before social media took off, my experience spending a year in China 10 years included the sense of being cut-off from what was going back home because my regular websites were routinely blocked: I even missed a launch of a Radiohead album until I heard it playing in a Starbucks in Hong Kong. Moving forward a few years, I've gotten used to getting sporadic comments on my older Facebook activities whenever my Shanghai based sister is travelling outside of China.
Lack of access to social media sites popular outside of China doesn't mean that Chinese web surfers don't micro-blog, upload and watch cat videos or keep up with friends online: there are just local versions of these services. To build an online audience in China and connect with users there, you'll have to leverage the local social media sites available. Here's list of approximate social media equivalents in and outside of China for major categories.