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.”