The New York Daily News said the celebrities, along with rapper Pharrell and members of the rock band Linkin Park, have had their cheeks swabbed to see if they are matches for Ayelet Galena, a 1-year-old girl suffering from the life-threatening disease dyskeratosis congenita.
The stars offered their help with the hope their fans will also get tested and a donor can be found for Ayelet.
"It started out with Rihanna tweeting, and then I asked 50 Cent. He has helped us before," Katharina Harf, the chief operating officer of DKMS, a German bone-marrow donor center, told the Daily News. "And then [Ayelet's] dad [advertising executive Seth Galena] got all these other artists and bands aboard."