We love to watch them in movies and on TV - but there is often much more than meets the eye when it comes to our favorite celebrities.  And when they choose to use their star power for good, the effect can be tremendous.  Here's a look at a few of Hollywood's finest that are using their celebrity status to shine a spotlight on finding a cure:

Robin Roberts. The "Good Morning America" host went public with her battle against breast cancer in 2008 and again when she was diagnosed with myelodysplastic syndrome, or MDS, a disease of the bone marrow that required Roberts to have a bone marrow transplant in 2012. Since then, Roberts has partnered with Be The Match to encourage folks to register for the National Bone Marrow donor program. When Roberts started talking to the world about the need for bone marrow donors, it caused an 1,800-percent spike in donor applications. The organization estimates that more than 44,000 potential donors have signed up since Roberts came on board.

Michael J. Fox. Fox was diagnosed with Parkinson's disease in 1991 and went public about the condition in 1998. Since that time, Fox has become the face of Parkinson's and has worked tirelessly via his namesake foundation to raise funds for a cure. The Michael J. Fox Foundation is now the largest nonprofit funder of Parkinson's drug development in the world.

Christina Applegate. Although she has starred in dozens of movies and television shows since, Applegate will probably always be best known for her teen character Kelly Bundy from the 80s sitcom "Married ...With Children." In 2008, the blonde bombshell was diagnosed with breast cancer and underwent a double mastectomy in her treatment. She since created Right Action for Women to educate other women about breast cancer and help cover the cost of treatment and screenings.  

Cindy Crawford. When Crawford was just 10 years old, her younger brother Jeff died of leukemia.  So it's no wonder that the supermodel has dedicated much of her time, money, and energy to help fund organizations and hospitals that are working towards a cure for childhood cancer. She is also a member of the celebrity board for Ronald McDonald House Charities and a celebrity supporter of Alex's Lemonade Stand, a nonprofit with the goal to "fight childhood cancer ... one cup at a time."

Seth Rogen. Actor/comedian Rogen started the charity Hilarity for Charity with his wife Lauren Miller to benefit the National Alzheimer's Association. Miller's mother suffers from the condition. In an interview with CNN, Rogen said "I think until you see it firsthand, it's kind of hard to conceive of how brutal it is." Hilarity for Charity is part comedy show and part musical concert with events held in Hollywood and at college campuses around the country.

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