Shares of Twitter Inc. /zigman2/quotes/203180645/composite TWTR +0.65% shot up 5.5% in premarket trading, toward 5 1/2-year-high territory, in the wake of blowout results from social-media rival Snap Inc. /zigman2/quotes/205087158/composite SNAP -2.14% . Twitter's stock is on track to open above the highest closing price seen since April 2015. Snap's stock rocketed 20% toward a record high before the open, after the company reported late Tuesday a surprise adjusted profit and revenue and user growth that was well above expectations. Fellow social-media company Facebook Inc.'s stock /zigman2/quotes/205064656/composite FB +3.16% rallied 3.4% ahead of the open, while shares of photo-sharing site Pinterest Inc. /zigman2/quotes/211319641/composite PINS -2.68% powered up 8.3%. The gains in social-media stocks comes while Nasdaq 100 futures /zigman2/quotes/210219788/delayed NQ00 +0.19% fell 0.1% and futures /zigman2/quotes/209948968/delayed ES00 -0.14% for the S&P 500 /zigman2/quotes/210599714/realtime SPX +1.62% eased less than 0.1%.