Tennis ace Andy Murray has joined an online campaign to help find a Chinese tennis player who has gone missing after accusing a government official of sexual assault. 

Murray tweeted that Peng Shuai's "whereabouts (are) currently unknown" after following her allegations, which have sparked concern many members of the professional tennis circuit. 

The two-time Wimbledon winner also linked to a video of Czech player Barbora Krejcikova speaking about her country's liberation from communism during the Velvet Revolution of 1989.

Other stars including Serena Williams, Naomi Osaka and Novak Djokovic are among those who have voiced concer for Peng's welfare.

China's foreign ministry claimed on Friday that it was unaware of the controversy.

Ministry spokesperson Zhao Lijian told reporters it was "not a diplomatic question and I'm not aware of the situation".

Peng, 35, a former Wimbledon doubles champion, wrote a social media post on 2 November accusing a former top government official of forcing her to have sex after playing tennis at his home.

Her original post on Weibo has been taken down.

An email said to be from Peng was released on Wednesday by CGTN, the international arm of government-controlled state broadcaster CCTV, but doubts have been raised over its authenticity.

It says the sexual assault claim "is not true" and adds: "I'm not missing, nor am I unsafe. I've just been resting at home and everything is fine".

Steve Simon, the head of the Women's Tennis Association (WTA) said it "only raises my concerns as to her safety and whereabouts".

"I have a hard time believing that Peng Shuai actually wrote the email we received or believes what is being attributed to her," he said in a statement.

"Peng Shuai displayed incredible courage in describing an allegation of sexual assault against a former top official in the Chinese government.

"The WTA and the rest of the world need independent and verifiable proof that she is safe. I have repeatedly tried to reach her via numerous forms of communication, to no avail."