A year ago, these three activists were ordinary Americans: a teacher, a school administrator and a temporary government employee. Like many others, they found a voice on social media to comment on the news, describe their personal experiences and relate the everyday struggles of blacks in America.

As their social media following soared during the Ferguson protests, so did their belief in the power of Twitter to dispute official statements that did not ring true. Eventually, they used Twitter and Tumblr to fund and mobilize protests and make demands on police departments and government officials. Their high-profile status also made some of them targets of intelligence monitoring and threats.

Here, Johnetta Elzie, DeRay Mckesson and Zellie Imani read their tweets from the past year and discuss how social media boiled after the fatal shooting by a police officer of 18-year-old Michael Brown in Ferguson, Mo., turning the nation’s attention to race and police conduct, and in the process changing their lives.

On Monday, officers with the Department of Homeland Security arrested Ms. Elzie and Mr. Mckesson during a civil disobedience protest at the federal courthouse in downtown St. Louis.

But on Aug. 8, 2014, the day before Mr. Brown was killed, Ms. Elzie was 25 and living in St. Louis. She had just finished a job as a phone interviewer for the United States Department of Agriculture and was considering going back to school. She had a community of friends and maybe 2,000 Twitter followers, and used social media to comment on topics like makeup, movies and sports.

On the day Mr. Brown died, Ms. Elzie drove to Ferguson and started tweeting and posting photographs and videos to social media. She has not stopped. A year later, she has more than 57,000 followers on Twitter. She is now an organizing member of the group WeTheProtesters.org, along with Mr. Mckesson.

Mr. Mckesson, 30, monitored Twitter during the first few days of last August’s protests from his home in Minneapolis, where he worked as a school administrator and had 1,000 or so Twitter followers. But after watching protesters in Ferguson clash with a militarized police force, he packed his car and tweeted, “En route to Ferguson.” In the months since, Mr. Mckesson has become a full-time protester and organizer, and a go-to source for reporters covering protests around the country. He has 200,000 Twitter followers.

On Aug. 12, 2014, Mr. Imani, a 30-year-old math teacher in Paterson, N.J., posted a link to his GoFundMe account, hoping to raise money for a plane ticket to St. Louis to join the protesters in Ferguson. He already had a respectable social media following as a commentator on his blog, Black-Culture.com. Altogether, Mr. Imani has traveled to Ferguson five times, with three of the trips financed by crowdfunding. He now has nearly 50,000 Twitter followers and helps organize NJShutitdown, a group protesting police brutality on college campuses in New Jersey.