Emerging market stock mutual funds are picking up steam again this year after taking a back seat to the U.S. stock market last year. In the past 15 years, emerging market funds have outperformed the S&P 500 and the MSCI EAFE index of developed markets by a wide margin. A $10,000 investment in emerging market funds on June 30, 1999, would have grown to $37,057 for investors by Aug. 8, 2014, according to Morningstar data.