Serena Williams joins a growing list of tennis stars condemning the disappearance of Chinese player Peng Shuai

• Serena Williams has called for an investigation into a Chinese tennis player who went missing.
• Peng Shuai has not been seen in public since accusing China's former vice premier of sexual assault.

Serena Williams has added her voice to a growing number of stars from the world of tennis expressing their concerns over the safety of Chinese player Peng Shuai.

On November 2, Peng accused former Chinese Vice Premier Zhang Gaoli of sexually assaulting her. She has not been seen or heard from since.

All mention of her accusation has also been scrubbed from Chinese social media platforms like Weibo.

On Wednesday, a letter claiming to have been written by Peng was released by Chinese state media saying she was fine, "not missing," and just resting at home.

Doubts were immediately cast about the letter's authenticity after it appeared only on the Twitter timeline of CGTN, an English language TV channel run by the Chinese state.

Steve Simon, the head of the WTA, said the letter only served to make him more worried about Peng.

Peng's disappearance has sparked outrage in the sport, with Williams on Thursday joining fellow stars like Novak Djokovic and Naomi Osaka in speaking out about Peng, and calling for an investigation into her whereabouts.

23-time Grand Slam winner Williams said the case "must be investigated" and urged people to "not stay silent."

Williams tweeted a picture of Peng with the hashtag #WhereIsPengShuai.

"I am devastated and shocked to hear about the news of my peer, Peng Shuai," Williams 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.

—Serena Williams (@serenawilliams) November 18, 2021

Williams is one of many high profile athletes in the game raising concerns for Peng's safety.

Men's world number one Novak Djokovic said it was "shocking" that she was missing, and Naomi Osaka tweeted a picture of Peng saying "censorship is never OK"

—NaomiOsaka大坂なおみ (@naomiosaka) November 16, 2021

Peng is one of China's most successful tennis players, having made a name for herself in doubles. She has won two Grand Slams, taking home the doubles competition at Wimbledon 2013 and the 2014 French Open, playing alongside Hsieh Su-wei.

In 2014, she was ranked number one in the world in doubles.