The 100 wealthiest people on the planet added $18 billion to their collective net worth this week as U.S. companies began reporting fourth-quarter earnings.

Facebook (Nasdaq: FB) Inc.’s co-founder and chief executive officer, Mark Zuckerberg, gained $1.3 billion, according to the Bloomberg Billionaires Index.

The largest social-networking service rose 10.3 percent during the week and hit a six-month high Friday. Investors are optimistic that the company will benefit from new advertising efforts to drive revenue. The 28-year-old is worth $14.6 billion, making him the 57th richest person in the world.

“Facebook has had a great week,” Matthew Houk, portfolio manager at Horizon Kinetics LLC, said in an e-mail. The New York-based firm manages about $7.2 billion. “However, one of the factors that we focus on is companies with long product life cycles. It remains to be seen whether Mark Zuckerberg can establish Facebook as an enduring product that will generate longer-term value for shareholders.”

Alcoa Inc. kicked off the reporting season on Tuesday, with the largest U.S. aluminum producer posting sales that beat analysts’ forecasts amid higher-than-expected prices for the metal. In China, inflation accelerated more than forecast to a seven-month high Friday as the nation’s coldest winter in 28 years pushed up vegetable prices, a pickup that may limit room for easing to support an economic recovery.

The Standard’s & Poor’s 500 Index gained 0.38 percent during the week to close at 1472.05 in New York. The Stoxx Europe 600 Index fell 0.26 percent, closing at 287.08.

Slim Remains No. 1

Mexican telecommunications magnate Carlos Slim, 72, remains the richest person in the world, with a fortune of $77.1 billion, down $157 million for the week. Second is Microsoft Corp. co-founder Bill Gates, 57, with $63.5 billion.

Europe’s richest man, Amancio Ortega, the 76-year-old founder of the Zara clothing chain, is No. 3 on the index with a net worth of $58.1 billion, $7.6 billion ahead of Warren Buffett. The 82-year-old chairman and chief executive officer of Omaha, Nebraska-based Berkshire Hathaway Inc. said U.S. banks have rebuilt capital to the point where they no longer pose a threat to the economy.

“The banks will not get this country in trouble, I guarantee it,” Buffett said in a phone interview last week.

The Bloomberg Billionaires Index takes measure of the world’s wealthiest people based on market and economic changes and Bloomberg News reporting. Each net worth figure is updated every business day at 5:30 p.m. in New York. The valuations are listed in U.S. dollars.