Shawn Mendes, a popular Viner with over 3 million followers (and a recent guest on Ellen) saw something that worried him when he did a meet and greet with his fans last month.
He saw his fans arrive with cuts on their arms.
He knew teens are often public with their acts of self-harm...after all, he had seen that #CutsForBieber had been trending on Twitter recently as well.
A basic search of "I cut my wrists" on Twitter brought up a stream of tweets promoting self-harm.
Alarmed, Mendes wanted to do something to help. So he went to DoSomething.org, a non-profit organization that promotes social change.
DoSomething takes any issue a young person (ages 13-25) cares about and gives them a platform to create powerful initiatives to help spread their cause. Most recently, the organization partnered with girl group Fifth Harmony. In the next year, the organization plans to help other YouTubers and Viners opportunities to work to create campaigns to get their fans to take action around a cause personal to them. What's more — they never ask young people for money. The causes and initiatives that surround them have very little financial implications. They're more about — aha — doing something.
In Mendes' case, he created #NotesFromShawn, a campaign that encourages young people to post positive messages in unexpected places to improve self-esteem and decrease thoughts of self-harm. 
The notes Shawn is holding say "you're talented,""you are beautiful," and "you are important."
And people have really responded. According to DoSomething, over 40,000 young people have participated, tagging their notes and stories with #NotesFromShawn all over social media.
Check out this comment on Instagram from a participant:
Here are some awesome tweets from people who were given notes from other teens participating in the initiative:
He even left behind some #NotesFromShawn when he was on Ellen:
There's more where this comes from on the #NotesFromShawn hashtag and you can check out DoSomething.org to learn more.