Facebook chief executive Mark Zuckerberg’s personal wealth has taken a hit, knocking him off the Bloomberg Billionaires Index, which ranks the top 40 billionaires in the world.

Since his company went public on May 18, the social network co-founder’s personal wealth on paper has dropped to $14.7 billion from $16.2 billion, Bloomberg reported after the company’s shares fell nearly 10 percent in Tuesday trading. The stock closed Tuesday at $28.84, and was trading slightly up Wednesday morning at $29.33.

It was the first time that Facebook shares had fallen below $30. The initial public offering earlier this month, one of the largest in U.S. history, is now also one of the worst-performing, having lost over 20 percent of its value in seven trading days.

Zuckerberg’s wealth is now $800 million below the last person on the list, Colombian banker Luis Carlos Sarmiento.
Trading at $29 per share, Facebook’s price-earnings, or p/e, ratio is high, at about 62.9 — and investors don’t see justification for paying such a high price for such a small return.