Twitter has been blocked in China since 2009 but is still used through virtual private networks (VPN).

Domestically, the Sina Weibo microblogging platform and Tencent’s WeChat messaging app are more widely used. But Chinese entities, including the state news agency Xinhua, use Twitter to reach audiences abroad.

Chen, who previously worked at Microsoft and Cisco , was brought in to lure more Chinese advertisers to Twitter. At the time, social media criticism focused on her early work with Chinese state-affiliated enterprises.

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“Now that the Twitter APAC team is working directly with Chinese advertisers, this is the right time for me to leave the company,” she wrote.

Twitter grew its Greater China advertiser base nearly 400% over the past two years, she wrote, making it one of the firm’s fastest growing revenue markets in Asia Pacific (APAC).

Twitter’s top Chinese advertisers have included Chinese smartphone maker Xiaomi, online shopping giant Alibaba Group , white goods producer Qingdao Haier and flag carrier Air China.

“We remain committed to this market,” Chen said, adding the company’s Hong Kong office would remain open.

Twitter confirmed it would retain the Hong Kong office to serve Hong Kong-based clients, but declined to provide further details on Chen’s departure.

For more on Twitter’s global restructuring, watch Fortune‘s video.

QUESTIONING THE VALUE

The end of Chen’s relationship with Twitter comes at a time when China is urging for greater internet curbs.

The country has condemned foreign social media as a hotbed for fake news and cyberterrorism, sending ominous signals to Western firms that are eyeing a piece of the Chinese market, home to the world’s largest population of internet users.

“When China’s economy was really on fire it created enough smoke to obscure the realities of what foreign tech companies were really going to be permitted to do here,” says Mark Natkin, managing director of Beijing-based Marbridge Consulting.

” you are getting more companies who are beginning to question the value of the investments they are making here.”

The popular but money-losing microblogging service Twitter has moved its Chinese ad sales and support activities to its APAC headquarters in Singapore.

Twitter has been undergoing a significant shakeup, and not only in Asia, announcing in October that it would cut more than 9% of its global workforce to keep costs down.

Parminder Singh, managing director for India, Southeast Asia and the Middle East, left the company in early November.

This story has been updated.