The delay and other problems in one of the most highly anticipated IPOs in recent years were a setback for Nasdaq, which competes with the New York Stock Exchange in listing stocks.
Facebook was expected to start trading at 11 a.m. Friday but didn't open until 11:32 a.m. Some investors didn't learn for hours whether their orders went through.
The CEO of Nasdaq, Robert Greifeld, said over the weekend he was "humbly embarrassed." It took Nasdaq until 1:50 p.m. to let its members know whether orders to buy or cancel were executed.
Facebook plunged 12 percent to $32.73 Monday, well below its initial offering price of $38.