By Allison Fine

When Sameer Bhatia, a 31-year-old Stanford graduate and Silicon Valley entrepreneur, was diagnosed with leukemia, doctors told him he had a one in 20,000 chance of finding a suitable bone-marrow donor.

Knowing those odds, his friends made it their goal to register 20,000 South Asians in a bone-marrow registry. Using social-media tools such as Facebook, Twitter, and YouTube, as well as traditional means, they managed to register 24,611 donors in a matter of weeks.

The Dragonfly Effect chronicles that effort. The book's co-author, Jennifer Aaker, says the success of Mr. Bhatia's story illustrates two essentials for social-media campaigns: Set a single, concrete goal, and never underestimate what a powerful narrative can do.

In the latest episode of Social Good, Allison Fine, the host, discusses these ideas with Ms. Aaker, a Stanford University business school professor.

Social media may make it easier than ever for more people to get involved in a cause, Ms. Aaker says, but it takes good stories to motivate people to act.

Allison Fine, a nonprofit leader and expert on technology and communications, discusses how charities and foundations can more effectively use social-media tools to spread their messages and raise money. Ms. Fine incorporates suggestions and questions from readers into her podcasts and invites you to e-mail her at afine@demos.org. Look for new installments on the first Thursday of every month.