Michelle Obama Joins #BringBackOurGirls Movement on Twitter

First lady Michelle Obama joined the #BringBackOurGirls movement on Twitter Tuesday afternoon.

The tweet is signed "-mo," which means the first lady herself penned the message.

The hashtag has become a rallying cry for women and men fighting for the release of nearly 300 girls captured by Boko Haram, a terrorist organization in Nigeria.

In the 23 days since the girls first went missing, the hashtag has been shared over a million times. Many prominent pols-from Hillary Clinton to Michelle Bachman-have joined the movement.

Earlier this week President Obama called the girls' abduction "heartbreaking" and "outrageous."