The pair are two of a number of celebrities who have joined a new campaign called Digital Life Sacrifice.

Part of Alicia Keys’ charity, Keep a Child Alive, the campaign aims to keep the celebrities off social networks from Tuesday (November 30) until the charity raises $1 million.

"It's really important and super-cool to use mediums that we naturally are on," Keys told the Associated Press.

Other supporters include Jennifer Hudson, Ryan Seacrest, Elijah Wood, Serena Williams, Kim and Khloe Kardashian, Janelle Monae and Keys' husband, Swizz Beatz.

They have all filmed "last tweet and testament" videos, which will be shown when the challenge begins.

(by Jason Gregory)