"Unfortunately, the leadership in China has not addressed this very serious issue in any credible way," WTA Chairman and CEO Steve Simon wrote in a statement distributed by the tour on Wednesday.
"While we now know where Peng is, I have serious doubts that she is free, safe, and not subject to censorship, coercion, and intimidation."
Mr Simon repeated his call for a "full and transparent investigation - without censorship" into Peng's accusations and took an unusually strong stand against China, which was supposed to be the site of several tennis tournaments next year, including the prestigious season-ending WTA Finals.
"In good conscience, I don't see how I can ask our athletes to compete there when Peng Shuai is not allowed to communicate freely and has seemingly been pressured to contradict her allegation of sexual assault," Mr Simon said.
"Given the current state of affairs, I am also greatly concerned about the risks that all of our players and staff could face if we were to hold events in China in 2022."
Beijing is set to host the Winter Olympics beginning on 4 February, and International Olympic Committee President Thomas Bach said late last month he spoke with Peng on a video call.
The IOC did not release a video or a transcript of the exchange and said only that Mr Bach reported she said she was well.
The IOC said in a statement that Peng appeared to be "doing fine" and said she had requested privacy.
The IOC did not explain how the call was arranged, although it has worked closely with the Chinese Olympic Committee and government officials to organise the upcoming Olympics.
Critics have suggested that Peng would not have called the IOC if she was truly free to speak.
"If powerful people can suppress the voices of women and sweep allegations of sexual assault under the rug, then the basis on which the WTA was founded - equality for women - would suffer an immense setback," Mr Simon said.
"I will not and cannot let that happen to the WTA and its players."
Source: WeChat/China Open
The Sport and Rights Alliance on Wednesday accused the International Olympic Committee (IOC) of acting irresponsibly over Peng's disappearance.
Prior to a 30-minute call with the IOC, the 35-year-old had not been seen for nearly three weeks since making her allegations.
"The behaviour of the IOC in relation to Peng Shuai's sexual assault allegations and disappearance has been irresponsible and shows just how hollow its understanding of human rights really is," Andrea Florence, acting director of the Sport & Rights Alliance, said in a statement.
"The IOC's eagerness to ignore the voice of an Olympian who may be in danger and to support claims of state-sponsored media in China shows the urgent and critical need for an IOC human rights strategy."
The Sport and Rights Alliance, comprised of non-governmental organisations and trade unions, aims to promote human rights in sport.
It said the IOC must put athletes' needs first with the 2022 Beijing Winter Games due to start in just over two months, and called upon it to use its influence to push China to investigate Peng's claims in an "independent and transparent" manner.
"The main purpose of the call was to enquire about the well-being and safety of Peng Shuai. In the 30-minute conversation, she was very clear in confirming that she is safe and well," the IOC said in a statement.
"Safeguarding the well-being of athletes is paramount to the IOC and the Olympic Movement. We have agreed to stay in touch, and she agreed to meet in Beijing in January."
The IOC added that Peng has "asked that her privacy be respected in all aspects".
The Human Rights Watch said last week that the IOC was more interested in keeping the Games on track than it was about athletes' welfare.
Senior IOC member Dick Pound responded on Tuesday, telling Reuters the criticism was "complete nonsense".
"What seemed to change after that (call) was all of the wannabes that were unable to get in contact with her sort of said 'well the IOC botched it' and 'this was all organised by the Chinese' and so on," Mr Pound said.
If you or someone you know is impacted by sexual assault, call 1800RESPECT on 1800 737 732 or visit 1800RESPECT.org.au. In an emergency, call 000.