Tennis stars around the world are now asking where Chinese tennis player Peng Shuai is after her sudden disappearance two weeks ago, shortly after she posted allegations of sexual assault against a former Chinese Communist Party official.

In a tweet on Nov. 18, American tennis star Serena Williams called for an investigation into Shuai's disappearance.

"I am devastated and shocked to hear about the news of my peer, Peng Shuai. I hope she is safe and found as soon as possible. This must be investigated and we must not stay silent," Williams wrote.

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And Serbian athlete Novak Djokovic, considered the best tennis player in the world, said Shuai's disappearance was "horrifying."

“I mean, a person is missing,” Djokovic told The Associated Press. “The whole community, tennis community needs to back her up and her family, make sure that she’s safe and sound because if you would have tournaments on Chinese soil without resolving this situation, it would be a little bit strange.”

Shuai published her allegations against former Vice Premier Zhang Gaoli, accusing him of manipulating her into having sex with him and emotionally abusing her in a relationship. The post has since been deleted and Shuai has gone missing.

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Japanese-American tennis player Naomi Osaka was one of the first high-profile celebrities to call attention to Shuai's disappearance on Nov. 16, writing #whereisPengShuai and that "censorship is never okay at any cost."

Since news of her disappearance broke, the Professional Tennis Players Association and Women's Tennis Association have called for an investigation, according to the AP. The United Nations has also called on China to investigate her disappearance, CNN reported.