China's ambassador to the United States should assist in "bringing about a satisfactory result" in regards to the missing tennis player Peng Shuai, Women's Tennis Association CEO Steve Simon wrote in a letter dated Friday.

Why it matters: Peng has not been seen in public since she accused China's former vice premier of sexual assault earlier this month. Tennis authorities have called for a full investigation into the allegations by the two-time Grand Slam doubles champion.

• Simon also told CNN Thursday that he is willing to pull WTA's business from China and lose millions of dollars to ensure Shuai's safety.

The latest: "Simply put, the WTA is at a crossroads in China," Simon wrote in his letter to Chinese Ambassador Qin Gang. "I hope I can rely on you to convey these messages to the leadership in China so this issue can be resolved."

• An employee of Chinese state TV on Friday posted photos of Shuai on Twitter in an attempt to quell concerns over her disappearance, AP reports.

This follow's China's state-owned broadcaster CGTN releasing an email purportedly from Peng on Wednesday, in which she claims she is resting at home and appears to deny her previous allegations.

• But Simon and other tennis stars have cast doubt on the email's authenticity.

What they're saying: "As Steve Simon has made clear, the WTA is at a crossroad in China," a WTA spokesperson told Axios. "We continue to call for independent and verifiable proof that Peng Shuai is safe and that her sexual assault allegation will be investigated fully, fairly and without censorship. If not, the WTA is prepared to do what is right."

• "Whether she was coerced into writing it, someone wrote it for her, we don't know," Simon told CNN earlier in the week. "But at this point I don't think there's any validity in it and we won't be comfortable until we have a chance to speak with her."

The big picture: Serena Williams became the latest top athlete to speak out about Peng's disappearance on Thursday, tweeting that she is "shocked and devastated" at the news.

Editor's note: This story has been updated with new details throughout.