Want to see change in 2019? Then roll up your sleeves and get started.

That was former president Barack Obama's new year's call to action on Twitter Saturday. Obama asked his followers to "make a commitment. Find something you want to change in your community and take the first step toward changing it."

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To motivate his followers, Obama shared a list of leaders who inspired him in 2018. Each of these leaders decided to help "build the better future" they wanted to see in the world, tweeted Obama.

This list included a range of change makers, such as Jonny Boucher, who lost 16 people to suicide and started a special Chicago coffee bar to help normalize conversations about mental health.

Baristas at his Sip of Hope cafe are trained to talk to people facing mental health challenges, and 100 percent of the shop's proceeds assist with suicide prevention and mental health education.

"Every revolution started with one person just being fed up and speaking up," explained Boucher in a video for the Obama Foundation.

Other leaders Obama featured included: Sandor Lederer and Moussa Kondo, non-profit leaders looking to attack corruption in countries such as Mali and Hungary; and Hong Hoang, an environmentalist who has led initiatives in Southeast Asia to push for energy conservation.

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Obama's tweets echoed the optimistic but practical message he shared last year in an interview for BBC Radio 4 with the U.K. royal family's Prince Harry.

Obama said at the time: "I can tell people what I genuinely believe, which is that if we take responsibility for being involved in our own fate, if we participate, if we engage, if we speak out, if we work in our communities, if we volunteer, if we see the joy that comes from services to others, then all the problems that we face are solvable."

Despite a harsh and troubled world, Obama explained to Prince Harry: "When you think of how much has changed and how much has gotten better, well then that has to make you optimistic, as long as you don't start thinking that any of us can sit back passively and assume it continues."

That said, grassroots action is key, as the former president reminded his followers Saturday. Small changes, made by individuals, can lead to massive transformation.

"What matters isn't the size of the step you take," Obama tweeted Saturday. "What matters is that you take it."

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