By Agence France-Presse
The Hollywood Reporter said that The New Yorker is set to publish an article later Friday in which Moonves, one of the most powerful men in Hollywood, is accused of sexual misconduct that includes unwanted kissing and touching.
The 68-year-old, who has transformed the fortunes of CBS, is one of America's highest-paid CEOs and one of the most powerful men implicated in the #MeToo reckoning against sexual harassment.
CBS shares tanked as talk of the story spread through Wall Street, dropping 6.6 percent to $53.72, before closing down 6.1 percent at $54.01.
Hours later, The New Yorker had still not published the article or responded to requests for comment.
"All allegations of personal misconduct are to be taken seriously," the CBS board of directors said in a pre-emptive statement.
"The Independent Directors of CBS have committed to investigating claims that violate the company's clear policies in that regard," they added.
The statement said the allegations were "recently reported" and go back "several decades." Upon conclusion of the inquiry, CBS said, "the board will promptly review the findings and take appropriate action."
The expose is reportedly written by Ronan Farrow, the 30-year-old whiz kid who shared a Pulitzer Prize with The New York Times this year for his reporting on fallen Hollywood mogul Harvey Weinstein, which galvanized the #MeToo movement to quash pervasive sexual harassment in showbiz and other industries.
Farrow took to Twitter, hours after the CBS share price first tumbled, to say that he does not comment on reporting he has not published.
"If you're reading about my work from secondary sources you're often not getting the full or correct story -- especially in cases where parties have an interest in downplaying or otherwise spinning," he wrote.
It remained unclear what impact the reports would have on a legal battle for control of the US television giant -- between the Redstone family, which controls CBS, and the board, chaired by Moonves.
Shari Redstone is a major shareholder of both CBS and Viacom, which owns cable networks such as Comedy Central, MTV and the movie studio Paramount. She is seeking merge the two companies. Moonves opposes the deal.
Forbes estimates his net worth at $700 million.
As chairman, he oversees all operations of the company, which include the CBS Television Network, premium cable service Showtime, and the Simon & Schuster publishing company.
He joined CBS in 1995 as president of CBS Entertainment from Warner Bros. Television, where his team developed hit shows such as "Friends" and "ER."
At CBS, he launched prime-time hits such as "Everybody Loves Raymond," "Survivor" and "CSI: Crime Scene Investigation."
He was promoted to president and CEO of CBS Television in 1998, and became chairman in 2003. He married his second wife Julie Chen in 2004.
In 2017, CBS was the most watched network in the United States, although it dropped into third place, behind NBC and Fox when it came to adults aged 18-49.
Last November, CBS News sacked Charlie Rose, at the time one of America's most respected TV journalists, after eight women told The Washington Post he had made unwanted sexual advances.