Celebrities are well-known for their powerful spheres of influence, but the rise of social media has allowed them to reach even further — and to inspire fans to action at the touch of a button.

In what's perhaps the greatest single call to action ever undertaken online, more than 150 entertainers, sports and fashion icons, and other notables are joining forces to help battle the devastating humanitarian crisis unfolding across East Africa. The worst drought in decades is hitting the region, impacting an estimated 12 million people. According to one U.S. official, hundreds of thousands of Somali children may die if more attention isn't paid to relief efforts.

Enter the "I'm Gonna Be Your Friend campaign spearheaded by the nonprofit Save the Children. Through a combination of Twitter and Facebook, celebrities involved in the effort will reach an estimated global audience of 700 million people. A short film, directed by award-winner Kevin MacDonald ("The Last King of Scotland"), has been released detailing the severity of the situation and featuring the song "High Tide Or Low Tide" by Bob Marley & The Wailers.

"Not one child should be denied food nor water," said Bob Marley's widow, Rita Marley. "Not one child should suffer. Along with Save the Children, we must stand up together as friends to put a stop to this, to feed our children and to save their lives."

Social media heavyweights like Lady Gaga, Justin Bieber, Ryan Seacrest, Britney Spears and many more have pledged to tweet and post about the campaign. Check out a three-minute clip of the campaign video below — or visit iTunes to download the full version. All money received will benefit Save the Children.