In just three years China's main microblogging site, Sina Weibo, has surpassed Twitter's entire global membership. More than 300 million Chinese are now tweeting, with millions more joining the national conversation every month. Shanghai-based journalist Duncan Hewitt finds out how microblogging is changing China.

Thanks to social media China is witnessing the emergence of a civil society of activists and justice-seekers. These 'netizens' are using Sina Weibo and other services to publicise miscarriages of justice, instances of corruption and environmental issues and force local and central government to act. The victim of a horrific attack shows Duncan how her desperate plea for redress on Sina Weibo led to a nationwide outcry. In Beijing he meets the dogs saved from a grisly death in the dog-eating South thanks to flashmob rescuers organised on Sina Weibo. And a group of mothers who met on Sina Weibo tell him about their campaign to promote breastfeeding across China. None of this was possible before the internet - but where will it all lead?

While some subjects are banned, Sina Weibo has also given Chinese people a new freedom to voice opinions on the news, their lives and their country.

Duncan meets the young people of Chengdu in Western China who are now part of a small but growing graffiti, hip-hop and dance scene. Just 15 years ago there was no way they could communicate with fellow fans, never mind the outside world. He'll visit Youku, China's YouTube, to watch their online X-Factor-style competition as it is filmed. And he'll meet the famous cartoonist using animation to ask questions about the materialism of the young and the detention of his fellow artist and friend, Ai Weiwei.