PARIS — Last Saturday, Thomas Mirallès donned a yellow vest in his hometown in southern France and headed out to protest President Emmanuel Macron and high taxes. Afterward, he and other demonstrators around the country returned home, just as they had done every weekend for the past month.
But though they were no longer gathered together in town squares and on the streets, Mr. Mirallès and many fellow protesters were far from dispersed. Away from the television cameras and police lines, they kept coordinating their actions online — mostly on Facebook.
While attention has been directed at the dramatic Saturday protests across France, much of the action occurs on the social network the rest of the week. Between Sunday and Friday, people like Mr. Mirallès broadcast Facebook Live sessions, share sensational videos of police aggression, host polls to crowdsource what issues to talk about during coming TV interviews, and plot their next moves.
“Both fuel each other,” said Mr. Mirallès, 27, a real-estate agent in Perpignan who moderates a Facebook group for protesters that has amassed more than 305,000 members. “Without Facebook there wouldn’t be such a movement, but the online activity is fueled by the energy in the streets.”
The Facebook interactions are feeding the so-called Yellow Vest protesters, which helps explain why so many have kept turning up every Saturday, forcing Mr. Macron to announce this week that he would cut taxes and increase some incomes. Inside the hundreds of Facebook groups that have popped up about Yellow Vests, the discussions — some of them rambling, others more intellectual — have offered clues as to what protesters have seized on each week.
This week, protesters in the Facebook groups were focused on Mr. Macron’s concessions. Many posted that the actions were insufficient and called for continued demonstrations, according to messages reviewed by The New York Times. The anger suggested that more demonstrations would occur this Saturday, though the numbers were likely to be smaller after a terrorist attack on Tuesday in Strasbourg in northeastern France.
“We are on the right track, let’s not give up,” wrote one user in the Facebook group La France en Colère, or Angry France, on Tuesday while sharing a news article suggesting that “tired” police forces might join the Yellow Vests.
France has a robust history of political protest, with or without Facebook. But looking inside the platform opens a window into the unruly nature of Yellow Vest conversations, with their disparate demands and competing agendas. Facebook has roughly 35 million monthly active users in France, or about 52 percent of the population, and many feeds are now crammed with images related to the protests.
In recent weeks, Facebook has turned several average citizens — nurses, truck drivers and small-business owners — into Yellow Vest influencers. Several have received over three million views for videos of them speaking into their phone, according to data from Crowdtangle, which tracks activity on Facebook.
But there is also plenty of misinformation, which provides fuel for more disaffection. After the Strasbourg shooting, in which a gunman killed four and wounded 10 others at a Christmas market, some users in Facebook groups falsely accused Mr. Macron’s government of using the attack as a diversion. That led some groups to temporarily turn off comments.
“Shooting in Strasbourg, a government machination to intimidate Yellow Vests,” one user posted on Tuesday. “It smells of smoke.” The post was later deleted.
Mr. Mirallès, who became the administrator last month of La France en Colère, said he tried to delete the most extreme material posted in the Facebook group. But that task is difficult, he said, given how fast-moving the activity is.
“There’s a huge amount of conspiracy theories, which is a shame,” he said. “We’re facing an increasing need of moderators and administrators. It’s a little complicated.”
Mr. Mirallès joined the Yellow Vest movement in October after growing frustrated with high taxes. He said he had reached out to La France en Colère to volunteer to help screen the posts flooding in as interest in participating in protests swelled. Within weeks, he was one of the group’s eight moderators, spending several hours a day responding to messages from fellow activists and reading through comments.
Steven Lebee, 31, a stay-at-home father from Haute-Savoie in the Alps who volunteers with Mr. Mirallès, said many protesters looked only to Facebook for information because of widespread mistrust of the mainstream media.
“There’s no other existing tool that could allow us to share so much information without being censored,” Mr. Lebee said. “The information we share is shared as we share it. There is no media distortion.”
But the proliferation of rumors and misleading posts on Facebook about the protests has led to concerns that the site is inflaming anger and making it harder for the authorities to find solutions.
Apart from the false information about the Strasbourg shooting, Yellow Vests last week shared misleading Facebook posts about a nonbinding United Nations migration pact signed by Mr. Macron in Marrakesh, Morocco, arguing that he would “hand France’s sovereignty over to the U.N.” Pictures falsely showing members of the police and military supporting the demonstrators were also shared hundreds of thousands of times.
On Twitter and the messaging platform Telegram, protesters also posted videos of French military vehicles with the false claim that they were being deployed to squash protests.
Facebook, which has grappled with scrutiny about how it spreads disinformation and distorts elections, published tips for spotting false information and said it had teamed up with fact-checking organizations in France.
“False news has no place on Facebook and we have doubled down on our efforts to prevent the spread of false information on our platform and to educate people on how to identify and signal this type of content,” the company said in a statement.
Twitter declined to comment. Telegram didn’t respond to a request for comment.
The spreading of misinformation has led some prominent Yellow Vest leaders to express concerns about the influence of social media in the protests.
“I’m not sure Facebook should have this role of amplification,” said Ingrid Levavasseur, 32, a nurse in Normandy who has become a spokeswoman for the movement. For many groups, she said, “it has gotten out of their hands.”
Facebook has long been used as a political organizing tool, but it has rarely fueled such a large protest movement inside a Western democracy, said Olivier Costa, a political scientist in Bordeaux and head of research at the National Center for Scientific Research. While the size of Yellow Vest protests may shrink after this week’s government concessions, the experience provides a template for future activism, he said.
For the Yellow Vests, it can be dizzying to “build such a movement and force a government to bend,” Mr. Costa said.
Those in the movement said the strength of social media was worth any drawback.
“Call Facebook a tool, a threat, a weapon, it’s hard to know,” Mr. Mirallès said. “But there would be no Yellow Vests today without it.”