Mark Zuckerberg -- Running Out of Cash

Mark Zuckerberg desperately needed to refill his wallet in Italy yesterday -- stopping by an ATM on the island of Capri ... after losing $1.5 BILLION on his plummeting Facebook stock ... in a matter of hours.

Facebook shares dropped 9.6% yesterday, finishing at a new low of $28.84 -- reducing Mark's net worth from $16.2 billion to $14.7 billion. All told, yesterday's drop raised the stock's losses to 24 percent ... making it the worst-performing large IPO in the last decade.

Yesterday's drop also cost Mark his spot on the world's 40 richest people list.