They include New York Mayor Michael Bloomberg, CNN founder Ted Turner and entertainment executive Barry Diller.
"The Giving Pledge" lists all the families and individuals who have committed to the project.
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The site says the pledge is a "moral commitment" not a "legal contract".
The campaign was started in June to convince US billionaires to give away at least half of their fortunes either during their lifetimes or after their deaths.
"We've really just started but already we've had a terrific response," Mr Buffett said in a statement.
He added: "The Giving Pledge is about asking wealthy families to have important conversations about their wealth and how it will be used."
Those who pledge their money to "philanthropic causes and charitable organisations" must publicly state their intention through a letter of explanation.
