The world\'s wealthiest people lost a combined $1.5 billion (Dh5.51 billion) last week as concerns about Greece\'s potential exit from the euro area and Spain\'s finances pushed the euro below $1.25 for the first time since July 2010. Facebook Inc. co-founder Mark Zuckerberg, 28, lost the most during the week, as shares of his Menlo Park, California-based social-networking company fell 16.5 per cent. Zuckerberg, who lost $3.2 billion, is the world\'s 35th richest person with a $16.2 billion fortune, according to the Bloomberg Billionaires Index. Mexican Carlos Slim, 72, gained $592.5 million during the week, as shares of his Mexico City-based tele-communications company America Movil SAB rose 2.4 per cent. Slim remains the world\'s richest person with a $66.1 billion net worth. Bill Gates ranks second on the index with a net worth of $59.8 billion — $6.3 billion behind Slim. Gates\' nest egg rose 1.1 per cent as shares of Redmond, Washington-based Microsoft Corp fell 0.72 per cent during the week. Three-quarters of Gates\' fortune is held outside of Microsoft. \"This is clearly a week where investors were exhibiting tremendous concern about the European and American economies and the prospects for returning to recession,\" Brian Wieser, a senior analyst at Pivotal Research Group LLC, said in a phone interview.