What do the International Monetary Fund, Louis Vuitton and Unilever have in common?

They are the among a clutch of Westerns institutions to join Weibo, China's most popular microblogging platform operated by Sina Corp, which has quickly become the place to be to promote, lobby and win over a large, important audience.

Twitter, Facebook, YouTube and other social media platforms popular abroad are blocked in China by a government worried that unfettered Internet access could undermine Communist Party rule.

But with more than 250 million mostly educated and white collar users, homegrown Weibo, which is similar to Twitter in that it allows users to post 140 character tweets and gather followers, is becoming a major influence in Chinese society.

Sina Weibo is becoming the national watercooler of China, said Sam Fleming, founder of Shanghai-based social media consultancy, CIC.

It's where people are sharing news, gossip. If you want to see what's happening in China, you open your Weibo account.

Christine Lagarde, head of the IMF, became the latest Western luminary to hop on the Weibo bandwagon last week.

To my Chinese speaking friends, here's a translation of my APEC Summit statement, Lagarde, wrote to her more than 120,000 followers on Monday.

A sophisticated social media strategy has become increasingly important for Western companies, with firms from Ford to Nestle increasing the proportion of their ad spend on the Internet and Facebook pioneering the mining of online data about users' likes and dislikes.

Now that trend is spreading to China.

More than influence, the ability for multinational corporations (MNCs) to reach the Chinese public directly with their message is one of the reasons why Weibo is growing in popularity, branding experts say.

It's the quickest way to communicate with Chinese audiences, said Rand Han, strategy director at Resonance China, a Shanghai-based social media digital agency.

When done right MNCs can quickly locate their target markets, gather information, habits, etc., from available data, and begin connecting almost immediately at significant reduction in costs versus traditional media.

For many of these companies and brands such as LVMH's Louis Vuitton, Unilever Plc and Coca Cola Co, China, with its burgeoning middle class, is a rapidly growing market for them and gathering insights via Weibo is essential in crafting branding messages.

A lot of our brands which are growing in China, the multinational brands we work with see Weibo as an immediate opportunity to set up a stake in a way that they then have a voice directly to their consumers, said Zaheer Nooruddin, lead digital strategist for Greater China for Burson-Marsteller.

BILL GATES TO MARIA SHARAPOVA

Celebrities have also caught the Weibo fever. Tom Cruise, who is affectionately known as A-Tang Brother in China, opened his account in February and now has almost 3 million fans.

Bill Gates, tennis star Maria Sharapova and actress Emma Watson have also taken to Weibo to promote their ventures and strengthen their fan base in China. Weibo says it has verified these accounts to be genuine.

The Chinese government has also taken note with numerous government departments and officials using the platform.

Shanghai's Communist Party chief said on Tuesday that government officials must respond swiftly to the needs of the people expressed through Weibo and other new media outlets and not hide their heads in the sand.

For foreign companies, the key benefit of Weibo is that it provides them with a clear dominant platform to go to in what was once a fragmented social media scene, experts say.

This has allowed foreign companies to move beyond the traditional marketing to more creative approaches, such interactive campaigning, that resonate with the Chinese people, they say.

If used properly, Weibo can also be effective in countering negative news.

Last week, official media reported that China's quality watchdog found toxic content in five brands of tea, including the Lipton brand.

In response, Unilever posted on its Weibo account (http://www.weibo.com/unilevercn)

that its Tieguanyin tea product was in line with national standards and included photo scans of tests done on its product.

People universally respond to honesty and true connection. If brands are willing to give (that), then they can turn a negative situation positive, Resonance China's Han added.

(Editing by Kazunori Takada and Alex Richardson)