How it works: Facebook users install a program called Causes. Facebook friends band together to solicit donations, promote advocacy and spread awareness for a cause.

The Internet is unparalleled in its power to quickly rally — and pressure — far-flung friends to participate, Green said. For example, with Causes’ popular birthday wish feature, users can ask their friends to donate money to a cause in lieu of presents. The birthday feature raises $20,000 a day for various causes.

Petitions are also effective. One petition to get insurance companies to cover genetic testing for breast cancer garnered nearly 3.5 million signatures. Causes does not take a cut of donations, but users can tip the service.

Causes also makes money from causes that are sponsored by nonprofits and others trying to reach more people, banner advertising and premium services that help nonprofits get more out of using the service.

The results: No gusher of funds for nonprofits yet, but Green has made significant progress in his quest to invent a new model for philanthropy. Causes has recruited 100 million Facebook users who have created 400,000 causes since May 2007.The median donation is $25. In all, Causes has raised $21 million for charity.