“If you’ve been sexually harassed or assaulted write ‘me too’ as a reply to this tweet,” Ms. Milano wrote.
Twitter promoted the #MeToo campaign on Moments, its platform of highlighted stories, and the hashtag went on to be used more than 500,000 times in its first 24 hours by people from all lines of work. Those taking part included the singer Lady Gaga; the actresses Rosario Dawson, Anna Paquin and Evan Rachel Wood; and the poet Najwa Zebian.
The Oscar-winning director Kathryn Bigelow applauded the movement. “The democratization of the spread of information can finally move faster than a powerful media mogul’s attempts to bury it,” she said by email.
The singer and actress Courtney Love accused the powerful Creative Artists Agency of punishing her after she raised questions about Mr. Weinstein’s behavior in 2005, and a recently unearthed video clip of Ms. Love making the charge has gone viral.
The model Cameron Russell started a thread on her Instagram account on misconduct by men in fashion. It has led to more than 50 models anonymously sharing their stories of harassment.
Kicked off by reports on the allegations against Mr. Weinstein, the outpouring came a little more than a year after The Washington Post published leaked excerpts from an “Access Hollywood” tape in which Donald J. Trump, then a candidate for president, boasted of groping women.
At issue now is whether or not Hollywood can continue its old way of doing business, with self-styled “outlaw” executives and auteurs getting away with sexual misconduct as lawyers and publicists protect them.
“I think it’s upsetting and devastating, all of the stories that have come out,” said Nina Jacobson, a film producer who was formerly the president of the Walt Disney Company’s Buena Vista Motion Pictures Group. “But I think the floodgates being opened is something that had to happen and that finally brings a subject to the surface that has sort of gone unchecked for countless years.”
Beginning with an article about the allegations against Mr. Weinstein that The New York Times published on Oct. 5, more than 30 accusers have stepped forward with charges of harassment, assault and even rape against the mogul. The police in New York and London have started criminal investigations. (Mr. Weinstein has denied engaging in nonconsensual sex.)
Fatima Goss Graves, president and chief executive of the National Women’s Law Center, said that, since the story broke, “we’ve gotten twice the volume of calls of people who have said they’ve experienced harassment.”
The reaction has also led some senior women in Hollywood to predict that their longtime calls for change may finally come to something.
“I don’t think this is going back to the status quo,” said Ms. Berman, the producer. “You’ll see that there will be improvement.”
The industry took a step toward that on Monday, when the Producers Guild of America moved to terminate Mr. Weinstein’s membership and issued a statement that seemed to catch up with the wave of disapproval sweeping social media.
“Sexual harassment of any type is completely unacceptable,” it said in part. “This is a systemic and pervasive problem requiring immediate industrywide action.”
On Saturday, the board of the Academy of Motion Picture Arts and Sciences stripped Mr. Weinstein of his academy membership. The move drew ridicule from the HBO comedy host John Oliver, given that it did no such thing in the cases of Mr. Cosby and Roman Polanski, who, in 1977, pleaded guilty to having unlawful sex with a 13-year-old girl and then fled the country.
“So congratulations, Hollywood,” Mr. Oliver said. “See you at the next Oscars, where — and this is true — Casey Affleck will be presenting Best Picture.”
The reference was cutting: Mr. Affleck, who won the best actor award at this year’s Oscars for “Manchester by the Sea,” had settled sexual harassment allegations made against him by two female producers in civil suits. He has denied the accusations.
Woody Allen served as the imperfect messenger for those cautioning against what he termed a “witch hunt.” His warning was in line with the thinking of some executives, who said they were wary of false accusations getting easy play on social media.
In breaking the news about the allegations, The Times and The New Yorker carefully corroborated women’s stories. Social media has no such checks and balances.
A spreadsheet listing men in the media business accused of sexist behaviors ranging from inappropriate flirting to rape surfaced last week and was circulated by email. The BuzzFeed writer Doree Shafrir weighed in on the list, writing of men who were said to be guilty of behaviors like leering: “Things do get complicated when you start lumping all this behavior together in a big anonymous spreadsheet of unsubstantiated allegations against dozens of named men.”
Ms. Jacobson, the film producer, said, “There’s an importance to a careful vetting and a careful reposting and not just a free-for-all.” She added that she was in favor of more information, not less, which is why, she said, the industry has to tackle the use of nondisclosure agreements.
“It clearly feels like we have to take the burden away from people to come forward,” she said. “They should not fear that, because you have an NDA, that you can’t speak up.”
Each successive case of a powerful man’s misdeeds bursting into the open helps to embolden the next round, the feminist Gloria Steinem said.
“When dealing with deep bias like racism and sexism, it usually takes more than one injustice — or even a few,” Ms. Steinem wrote in an email. “The Weinstein scandal would probably have been taken less seriously if Cosby, Ailes and others hadn’t come first and been within easy memory.”
Melinda McGillivray, who stepped forward last year to accuse Mr. Trump of groping her at his Mar-a-Lago club in Florida in 2003, told BuzzFeed last week that Ms. Paltrow and Ms. Jolie had an impact her accusation did not because of their star power. (Mr. Trump has denied harassment accusations.)
Mr. Trump’s election had put some women here on guard against a return to male misbehavior that was more common 40 years ago. And one list circulating among ranking female executives in the industry has tracked a string of promotions of men to senior jobs — at Apple and AMC, Sony and Hulu, Fox and CBS — amid fear that progress for women has stalled since November.
“Most of the available senior management television jobs this year have gone to men,” said Katie O’Connell, a chief executive of Platform One Media, and formerly the chief executive of Gaumont Television. “While those men were all qualified, it does highlight diminished access for these highest-level positions for women in 2017.”
As part of the general reaction to the articles on Mr. Weinstein, the Hollywood & Highland shopping center removed from its 17-year-old “Road to Hollywood” public art exhibit a daybed that some have taken to represent the proverbial “casting couch” — the symbol of ritualized abuse that studio chiefs meted out in trading roles for sexual favors. It was removed because it had “attracted increased public attention and it has been threatened with damage,” a spokeswoman for the mall said.
The artist behind the installation, Erika Rothenberg, said in an interview that her work was not meant to invoke the casting couch. Referring to Mr. Weinstein’s case, she said she was “completely sympathetic to people who have feelings about this, who are angry about this.”
Nonetheless, she said she hoped the daybed would return. “I don’t think this piece is the problem,” Ms. Rothenberg said.