US futures tumble after UK votes to quit EU; UK PM says plans to resign By: CNBC.com News June 24, 2016 at 03:43 AM EDT U.S. stock index futures tumbled on Friday, as results from Thursday's referendum showed the U.K. has voted to leave the European Union. Read More >> Related Stocks: Dow Industrials SPDR PowerShares QQQ S&P 500 Ishares Core ETF SPDR S&P 500 ETF Trust Sentinelone Inc Cl A The Finish Line, Inc. - Class A Common Stock