Top 400 were largely the same people thanks to buoyant stock market

Facebook founder and CEO was ranked number 10 with $34billion fortune

Bill Gates was top of the list for the 21st year, with $81.2billion to his name

America's wealthiest are worth more than ever - with the top 400 billionaires worth a breataking $2.3trillion, according to the latest edition of the Forbes 400.

The renowned rich list was again topped by Bill Gates - the richest American for the past 21 years - whose fortune was $81.2billion.

But the Microsoft founder, 58, had newer technology billionaires snapping at his heels, including Facebook CEO Mark Zuckerberg, who broke the top 10 for the first time having gained $15billion in the past year.

Scroll down for the top 40 and the size of their fortunes

Old tech, new tech: Bill Gates, the Microsoft founder, topped the Forbes 400 with his $81.2billion fortune, while Facebook CEO Mark Zuckerberg, 30, hit the list's top 10 just a decade after founding the social network while in college

THE RICHEST OF THE RICH: FORBES 40 WEALTHIEST AMERICANS Sage of Omaha: Warren Buffett remained the second-richest American, despite giving billions more away 1 Bill Gates $81.2billion 2 Warren Buffett $68billion 3 Larry Ellison $48.6billion 4 Charles Koch $42.9billion 4 David Koch $42.9billion 6 Christy Walton & family $38.3billion 7 Jim Walton $36.6billion 8 Alice Walton $35.2billion 9 S. Robson Walton $35.2billion 10 Mark Zuckerberg $34.7billion 11 Michael Bloomberg $34.3billion 12 Sheldon Adelson $31.7billion 13 Larry Page $31.7billion 14 Sergey Brin $31.2billion Walmart wealth: The top 10 featured three members of the Walmart dynasty - #6 was Christy Walton (left), the world's richest woman, #7 was Jim Walton (center) and #8 was Alice Walton (right) Tech boss: Amazon CEO Jeff Bezos, #15 15 Jeff Bezos $29.9billion 16 Carl Icahn $26billion 17 George Soros $24billion 18 Steve Ballmer $22.3billion 19 Forrest Mars Jr $22.2billion 19 Jacqueline Mars $22.2billion 21 John Mars $22.2billion 22 Len Blavatnik $21.6billion 23 Phil Knight $21.1billion 24 Michael Dell $17.5billion 25 Harold Hamm $17.5billion 26 Paul Allen $17.1billion 27 Charles Ergen $16.9billion 28 Laurene Powell Jobs & family $16.4billion Media mogul: Rupert Murdoch is 33rd on the list 29 Anne Cox Chambers $15.8billion 30 Donald Bren $15.3billion 31 Ray Dalio $15.2billion 32 Ronald Perelman $14.4billion 33 Rupert Murdoch & family $13.9billion 34 John Paulson $13.7billion 35 Jack Taylor & family $13.6billion 36 Abigail Johnson $13.3billion 37 James Simons $12.5billion 38 Andrew Beal $11.9billion 39 Patrick Soon-Shiong $11.9billion 40 Philip Anschutz $10.9 billion Advertisement

The 30-year-old social network billionaire had his wealth set at $34.7billion, just over a decade after he launched thefacebook.com from his Harvard dorm room.

His huge increase in wealth in the past year - the biggest in the Forbes 400 - netting him a nine-place gain from twentieth in 2013, when his wealth stood at $19billion.

Not far behind Zuckerberg were Google founders Larry Page (#13, $31.7billion) and Sergey Brin (#14, $31.2billion), Amazon CEO Jeff Bezos (#15, $29.9billion).

YOUNG AND LOADED: HOW SCIENCE AND SOCIAL MEDIA HELPED 11 UNDER-40s INTO THE ELITE WEALTH CLUB A keen grasp of technology - especially social media - is the key ingredient that opened the doors to unimaginable wealth for the under-40s of the Forbes 400 list. Top of the pile is Mark Zuckerberg, whose $34billion fortune sees him at spot 10 on the list aged just 30. Golden youth: Elizabeth Holmes, left, and Dustin Moskovitz, right, are both 30-year-old billionaires He is followed by former Harvard roommate Dustin Moskovitz, whose Facebook fortune netted him $8.2billion. While not nearly so rich, he is a few months younger than Zuckerberg, Also just out of her twenties is Elizabeth Holmes, 30, whose $4.5billion comes from blood testing company Theranos, which she founded after dropping out of college. Facebook, Twitter, WhatsApp, Uber and GoPro have also helped most of the other under-40s on the list into their spots. Advertisement

Another long-standing giant on the Forbes list is investment guru Warren Buffett, 84, ranked second with a $68billion fortune.

SWIPE RIGHT FOR CASH: APP FOUNDERS JOIN THE UBER-RICH The Forbes 400 list saw an influx of app founders this year, after mobile technology took another leap. The founders of the WhatsApp messaging service, Jan Koum (#61, $7.7billion) and Brian Acton (#158, $3.4billion), joined the list after Facebook bought their company for $19billion in February. WhatsApp billionaires Jan Kuom (left) and Brian Acton (right) joined the Forbes 400 this year Travis Kalanick, (#202, $3billion), who invented taxi app Uber, also found himself among the rich after his company was valued at $18.2billion this summer. Twitter cofounder Evan Williams (#178, £3.2billion), also sailed into the list on the back of the company's IPO in November, which valued the company at $25billion. He joins Jack Dorsey, former Twitter CEO, on the list. Dorsey was ranked 240th with a $2.6billion fortune. Advertisement

The so-called Sage of Omaha, CEO of investment firm Berkshire Hathaway, saw his wealth rocket this year thanks to a buoyant stock market, which took shares in his company above $200,000 a piece.

He managed to keep his coveted spot near the top despite having reportedly given away some $23billion in his lifetime.

Even the lowest entrant to the Forbes 400, biotechnology magnate Alan Auerbach, has $1.4billion to his name, and the magazine reported that 113 U.S. billionaires were deemed too poor to be included.

The $2.3trillion total worth of the list is a hike of $270billion from last year, an increase of almost 12 per cent. The average fortune on the list was $5.7billion, up from $5billion last year.

More than three quarters of the list saw their values climb in the past year, with only 36 losing money.

Despite the clear influence of internet and tech phenomena such as Facebook and Amazon in the upper echelons, the top 20 was still dominated by long-standing titans of the American economy.

Joint for fourth place on the list - at $42.9billion each - were Charles and David Koch, overlords of Koch Industries, a giant company with interests in the oil industry, building and manufacturing.

The were followed by members Walton family - Christy, Jim and Alice - who derive astonishing fortunes - $38.3billion, $36.6billion and $35.2billion respectively - from the Walmart retail empire founded by Sam Walton.

The most dizzying rise on the list was from GoPro founder Nick Woodman, whose camera company has seen his wealth increase threefold since last year, giving him a total of $3.9billion thanks to huge sales of his devices, beloved of extreme sportsmen.