30 Celebrities Lip-Sync Heartfelt Song By Dying Teen

Zach Sobiech, 18, became a YouTube star in December when "Clouds" — a catchy, heartwarming song he wrote after being given a year to live — went viral with over 2.6 million hits.

After being diagnosed with a rare bone cancer, Zach wrote lyrics such as "Go up in the clouds because the view's a little nicer up here, my dear" to comfort himself — but quickly won over the hearts of millions, including Hollywood celebrities.

On Monday, stars such as Brian Cranston, Sarah Silverman, Ashley Tisdale, Chris Pratt, Anna Faris, Jason Mraz, Jenna Elfman, the Lumineers, Rachel Bilson, Ed Helms, among others posted a video response lip syncing to Zach's voice, singing "Clouds."

The crew of celebs featured in the video was assembled by "Office" star Rainn Wilson and Justin Baldoni, who directed a short documentary about Zach for his online reality series, "My Last Days," which runs on Wilson's SoulPancake YouTube channel.

First, meet Zach and watch him sing "Clouds" below:

Now watch 30 celebrities lip-sync Zach's song, dedicating it to him: