Serena Williams is joining the growing calls of concern over the whereabouts of Chinese tennis player Peng Shuai.

“I am devastated and shocked to hear about the news of my peer, Peng Shuai,” she wrote. “I hope she is safe and found as soon as possible.

“This must be investigated and we must not stay silent. Sending love to her and her family during this incredibly difficult time.”

Peng has not been seen in public since before Nov. 2, when she posted to Chinese social media site Weibo allegations of sexual assault by a former Chinese Minister. In the post, which has since been deleted, she revealed an on-and-off affair with Zhang Gaoli that later turned non-consensual.

On Monday, WTA chairman and CEO Steve Simon issued a statement, calling the events “of deep concern” and calling for an investigation into the matter. Despite several sources assuring him Peng is safe in China, no one associated with the WTA Tour has been able to contact her directly to confirm the reports.

On Wednesday, an email was shared by Chinese state press, reportedly from Peng. The email says that Peng is “not missing, nor am I unsafe.”

In a statement issued by the WTA, Simon expressed his concerns over the statement, saying it “only raises my concerns as to [Shuai’s] safety and whereabouts.” He later added that he had a hard time believing the email was written by Peng.

Fellow Grand Slam champion Naomi Osaka has also expressed concerns over Peng’s safety.