Although she didn't know it at the time, Hernandez had become part of a cutting-edge trend: peer-to-peer health care. Type the words "kidney donor" in Facebook's search engine, and you'll get some sense of the movement's scope: Hundreds of pages come up. One shows a middle-aged father of two, another a stylish Seattle newscaster. There's a 59-year-old grandmother and a 26-year-old woman who, according to her bio, "does not have much time left" if she doesn't receive a new kidney soon. Stories with happy endings have hit the news—like the one about the former mayor of East Haven, CT, who in 2010 donated a kidney to a constituent she had friended on Facebook.

Millions of Americans — one in five, a 2011 survey reported — turn to social media for health information. A study by the Pew Research Center's Internet & American Life Project found that one in four Internet users with high blood pressure, diabetes, or other chronic conditions has gone online to find people with the same health problems.

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