Their mission started modestly: Challenge people around Massachusetts, and maybe throughout New England, to write “UNIFY” on the back of their hand and post a selfie covering their mouth with that hand.

But the kids who came up with the idea don’t think small. One suggested they aim to reach all 50 states. Another said, how about 50 countries. This was, after all, a problem that had no geographic boundaries.

The message the selfie conveys is simple: Don’t be silenced by bullying.

Thirteen-year-old Julianna Zemba knows a lot of people who have been bullied. She’s been made fun of for her height. Her older brother was harassed by a group of popular boys. Other friends were picked on for what they wore or who they hung out with.

So she and her family decided to do something about it.

Her father, Edward Zemba, who had been deeply disturbed by the suicides of two bullied teenagers in their community in recent years, created a nonprofit in January, Unify Against Bullying, with the goal of showing kids they didn’t have to take on bullying alone. It has a student board, so kids are involved in all the decision-making.

“The selfie challenge came from talking to kids about how social media has been weaponized by kids who want to use it for negative means to hurt other kids,” Zemba said. “Let’s see if we can take the power of social media and use it to empower. Our whole goal is to empower the kids to give them a sense that they can make a difference. That’s a huge part of bullying, they feel like they have no power.”

While bullying has always been an issue among teens and adolescents, cellphones and social media have made it more pervasive, and in many cases, more targeted and definitely harder to ignore.

The selfie challenge ends Saturday — 50 days since Oct. 1, the start of National Bullying Prevention Month. And they’re so close to their goal. Unify selfies have been tweeted, or posted on Instagram or Facebook from 39 states and 47 countries. By pure happenstance, Julianna ran into actor Chris Evans (a.k.a. Captain America) and asked him to pose for a unify selfie. They’ve come from as far away as Syria, Afghanistan, China and the Philippines. They’ve spanned religions and races and ages and gender.

They’re still missing selfies from West Virginia, Alabama, Kentucky, Iowa, Wisconsin, South Dakota, North Dakota, New Mexico, Wyoming, Idaho, Nebraska, so if you live in one of those states, or know someone who does, let’s get these kids to their 50-state goal.

Before Saturday’s deadline, Julianna is also planning to challenge future first lady Melania Trump to post a selfie. The soon-to-be first lady named cyberbullying as the issue she’ll focus on in the White House.

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