When marketing professor Jennifer Aaker heard about Samir Pendse's relapse into leukemia, she knew how to help.

Aaker's Facebook page and email about the 18-year-old's case, which included a picture of him smiling, said that a bone marrow transplant could save Samir's life. The social media outreach drew 62 people last Sunday from the Fremont Hindu Temple to do cheek swabs to see if they had compatible bone marrow—several more potential donors than his family could have gathered on their own.

"When you learn about something from your friends or people you trust through email or Facebook, it's much more persuasive than a message coming from a corporation or someone you don't know," said Aaker, who teaches at Stanford's Graduate School of Business.

Aaker is now working with students from Stanford's Haas Center for Public Service, using social media to get 100,000 people signed up with the national bone marrow registry.

Aaker got the idea from her former student Robert Chatwani, who used social media to find a bone marrow match for his friend, Sameer Bhatia. Bhatia had a 1 in 20,000 chance of finding a donor.

"I used to think social networking was a waste of time," said Aaker. "I thought the more time you spend on Facebook and Twitter, the more narcissistic and self-involved you become. But it became clear that social media can be used to amplify altruism and create social good in the world."

Aaker's book, The Dragonfly Effect, details the use of social media to rally large numbers of people to take action for a cause.