Rapper Tyga is on a festive mission to help a sick fan find a kidney donor. The Rack City hitmaker met 16-year-old Isael Lopez during a recent visit to Los Angeles Children's Hospital, and he was so moved by the youngster's story that he has rushed to help. The star has taken to Instagram.com to share a snap of Lopez, writing, "Spent my day Today with one of my biggest fans Isael Lopez, a 16 year old Los Angeles Children's Hospital patient who is in need of a kidney transplant. He helped me give holiday gifts to teens and tots battling cancer. Call 323 3615454 to find out if you are a kidney match for Isael. Www.donatelife.net."