Viviandan and MiuMiu are fashion-obsessed twin sisters from China who document their glamorous lives on social media -- trying on a gauzy Vera Wang wedding gown, or taking in a Dior runway show. They have a sizeable following on Facebook-owned Instagram, at 381,000. That's nearly on par with big brands they're tagging in posts, like Chloe (426,000 followers) or Vera Wang (515,000.)

But on Weibo, China's Twitter, their fan base is a whopping 4.2 million. There are lots of bots on Weibo, granted, but the scale of China's local social media is nonetheless massive. And Western platforms haven't been able to match that, even in the rare cases when they weren't blocked by China's great firewall.

For years, Instagram was one of those exceptions, remaining accessible well after Facebook, YouTube and Twitter were blocked. It went dark in late September, presumably because users were sharing photos of pro-democracy protests in Hong Kong. (The Chinese government never explains changes to the firewall.)

And while the Instagram shutdown is yet another blow to freedom of speech and information, cutting off one of the last links between China and the global internet, experts say the marketing industry won't be heavily affected by the loss. Brands have mostly used Chinese platforms to reach Chinese consumers, because that's where the big user numbers are.

What it means for brands

Marketers on Instagram in China were mostly experimenting, intrigued by its potential for reaching Chinese consumers with a creative, global mindset.

Social@Ogilvy asked in a presentation early this year whether Instagram might be "the only Western social platform relevant in China," and noted that it had the advantage of connecting the Chinese public to global users, unlike Chinese social media. It also pointed out a few local brands using it, including trendy Hong Kong retailer I.T, which has many mainland locations. Instagram's Chinese key opinion leaders include the fashion-blogging twins and another style maven, Han Huo Huo, who has 279,000 followers.

But most marketers have focused on Weibo (156.5 million monthly active users, presumably mostly in China) and social app WeChat (438 million, inside and outside China.) Instagram, which has 200 million monthly active users worldwide, hasn't discussed its usage or growth in China lately, though download records from AppAnnie suggest it has had a modest but growing following. The social network didn't respond to an email request for comment.

"It's a shame that Instagram is gone, but for brand marketers in China it's a relative non-event, for the fact that they haven't made big investments in the platform," said Chris Baker, founder of Totem, a social media management agency focused on China, which has researched local apps similar to Instagram. One is PaPa, which offers photo filters as well as sound effects. Another is Meipai, which turns video clips into music videos.

The mysteries of Instagram

Why was Instagram able to stay online in China until now? Perhaps it's because people in China often used Instagram for editing photos but used other platforms to distribute them, Mr. Baker said. Instagram-retouched photos can be shared directly on Weibo.

The company appears to have been keeping a low profile in China, too, possibly to stay under authorities' radar.

Facebook, YouTube and Twitter were blocked years ago in China (savvy users can still access them by circumventing the firewall through VPNs, or virtual private networks). Japan's Line and Korea's KakaoTalk recently succumbed as well. Even Google has been heavily affected.

Of major U.S.-based social media, LinkedIn remains viable in China, because it agreed to play China's game. Some people who post about sensitive topics get messages that their content is banned in China and cannot be seen by members there.

Despite the popularity of Chinese social media with marketers, it's censored, of course. Censorship and crackdowns on microbloggers have hurt Weibo's reputation, and many users say they have gravitated to WeChat because it feels more private, as their posts are shared only with friends. WeChat is being monitored and controlled nonetheless: Users reported that when they shared photos from Hong Kong during the protests, friends on the mainland couldn't see them.