NEW YORK - Facebook's Mark Zuckerberg was the biggest dollar loser in Forbes' latest ranking of the 400 wealthiest Americans.
His company's lacklustre IPO in May resulted in a huge drop in market value that cut the value of his shareholdings nearly in half, costing him $US8.1 billion in net worth. That dropped the world's youngest billionaire ever from No.14 on the list to No.36.
But although Zuckerberg lost more money than most people will make in many lifetimes, his net worth still totals an estimated $US9.4 billion, according to the magazine.
Microsoft co-founder Bill Gates remains the nation's richest man by far, as the tech and philanthropy giant took the top spot on the Forbes 400 list for the 19th year running, with a net worth of $US66 billion.
Investor Warren Buffett, the head of Berkshire Hathaway, again took second place with $46 billion, while Oracle co-founder Larry Ellison remains third with $US41 billion and brothers Charles and David Koch, co-owners of Koch Industries tied for fourth with $US31 billion.
Forbes said the rich mainly got richer in 2012, with net worth rising for 241 members of its list and shrinking for only 66. Rising stock prices, a rebound in real estate values and rare art prices helped.
But for social media moguls, it was the tough year. Zynga's Mark Pincus and Groupon's Eric Lefkofsky dropped off the list entirely.
Meantime, more members of the Walton family, the founders of Wal-Mart Stores, moved up into the Top 10, displacing investor George Soros and Las Vegas Sands founder Sheldon Adelson.
New York City Mayor Michael Bloomberg, who made his fortune with the financial data services firm Bloomberg, is also back with the top dogs at No. 10 with an estimated net worth of $US25 billion.
Twenty newcomers joined the list, which required $US1.1 billion in net worth for entry, up from $US1.05 billion a year ago.
Among the freshly minted are Shahid Khan, owner of the NFL's Jacksonville Jaguars, at No. 179; Judy Faulkner, founder of health records firm Epic Systems, at No. 285; Andrew & Peggy Cherng, the husband and wife team behind restaurant chain Panda Express, at No. 239; and Twitter creator Jack Dorsey at No. 392.
There are 45 women on the list, up from 42 a year ago, including Oprah Winfrey at No. 151.
The top 10 people on this year's Forbes 400 list are:
- Bill Gates, $US66 billion
- Warren Buffett, $US46 billion
- Larry Ellison, $US41 billion
- Charles Koch, $US31 billion
- David Koch, $US31 billion
- Christy Walton & family, $US27.9 billion
- Jim Walton, $US26.8 billion
- Alice Walton, $US26.3 billion
- S. Robson Walton, $US26.1 billion
- Michael Bloomberg, $US25 billion