Facebook co-founder Mark Zuckerberg is no longer among the world’s 10 richest technology billionaires.

The 28-year-old’s fortune dropped by $423 million as shares of the world’s largest social media company fell 4 percent to $20.04 in trading. Zuckerberg is now worth $10.2 billion. He is about $400 million behind James Goodnight, the co-founder of Cary, North Carolina-based software maker SAS Institute Inc., who now ranks as technology’s 10th- richest person, according to the Bloomberg Billionaires Index.

“From an emotional standpoint, he might care,” said Ron Florance, managing director of investment strategy for Wells Fargo Private Bank, in a telephone interview from Winston-Salem, North Carolina. “He’s much more worried about maintaining Facebook’s market share in the social media space than the day- to-day valuation swings of his company stock. He’s not worried about going broke.”

Facebook shares have fallen 47 percent from their initial public offering price of $38. The Menlo Park, California-based company last week reported earnings that showed slowing revenue growth.

Larry Yu, a company spokesman, didn’t respond to a phone call requesting comment.

Zuckerberg’s fortune is based on his ownership of 503.6 million shares of Facebook, including 60 million options that have an exercise price of 6 cents a share. He also has about $150 million in cash and other liquid assets.

Goodnight, 69, co-founded SAS in 1976, and is worth $10.6 billion. The company is the world’s largest closely held software maker and generated revenue of $2.7 billion in 2011, up 12 percent in a year.

SAS is valued at $15.8 billion, according to data compiled by Bloomberg. The valuation is based on the average enterprise value-to-earnings before interest, tax, depreciation and amortization multiple of five publicly traded peers. A premium has been applied, based on recent transactions in the software industry.

Goodnight, who holds two-thirds of SAS, also co-owns the Prestonwood Country Club in Cary, North Carolina, and has collected dividend payments over more than three decades.

Microsoft co-founder Bill Gates is the richest technology billionaire in the world with a net worth of $61.6 billion, according to the index.