The new option was announced Tuesday by Facebook CEO Mark Zuckerberg as a way to boost the number of potential organ donors. By the end of the day, 6,000 people had enrolled through 22 state registries, according to Donate Life America, which promotes donations and is working with Facebook. On a normal day, those states together see less than 400 sign up.

The response "dwarfs any past organ donation initiative," said David Fleming, chief executive of Donate Life America, in a statement.

The Facebook feature allows users to share their decision to be an organ donor on the website. More than 100,000 did that by Tuesday night, according to Facebook, which is working with Fleming's group to encourage Facebook users to also officially register as donors with their state.

Facebook, a social network site founded in 2004, has 526 million daily users around the world. It was Facebook's idea to add the option, after Zuckerberg took a personal interest in the issue, Michel said. The feature is available in the U.S. and the United Kingdom.

As with some personal information on Facebook, organ donor status can be kept private or shared publicly or only with friends.

More than 114,000 Americans are currently on waiting lists for transplants of kidneys, livers, hearts and other organs, according to United Network for Organ Sharing (UNOS), the organization that runs the nation's transplant system. More than 6,600 died last year waiting for an organ.

According to UNOS, 43 percent of adults in the U.S. are registered as donors. Organs can only be used though under certain circumstances, such as when someone dies from a major head injury and a ventilator can keep the organs viable. Less than 1 percent of U.S. deaths annually are under such circumstances. And sometimes the opportunity is lost because family members didn't know about the person's wishes on organ donation.