* Twitter rallies in premarket after blockbuster results
* Investors look ahead to GDP data, Fed statement
* Futures up: Dow 37 pts, S&P 4.75 pts, Nasdaq 13 pts
By Ryan Vlastelica
NEW YORK, July 30 (Reuters) - U.S. stock index futures rose on Wednesday as investors sought bargains following a period of weakness and looked ahead to data on economic growth and comments from the Federal Reserve following its latest policy meeting.
* U.S. second-quarter economic growth data will be released at 8:30 a.m. EDT (1230 GMT), with GDP expected to have grown 3 percent. That would represent a sharp turnaround from the weather-impacted first quarter, when the economy contracted 2.9 percent.
* The July ADP National Employment report on private sector employment will be released a little earlier, at 8:15 a.m., and is expected to show 230,000 jobs created in the month, down from June's 281,000.
* Twitter Inc surged 27 percent to $49 in heavy premarket trading. On Tuesday, the social media company reported monthly active users had risen a better-than-expected 24 percent in the second quarter and gave a revenue outlook that was above forecasts.
* The results could bolster support for Internet and other social media stocks, assuaging concerns the group is overpriced. Facebook Inc, which also posted strong results this quarter and is up almost 35 percent this year, rose 0.8 percent to $74.31 before the bell.
* Among other earnings, American Express Co late Tuesday reported adjusted earnings that were in line with expectations, while WellPoint Inc's earnings beat expectations.
* At 2:00 p.m. (1600 GMT), the Federal Open Market Committee will release a statement as it concludes its latest policymaking meeting. The central bank is widely expected to trim its monthly asset purchases to $25 billion from $35 billion, which would leave it on course to shutter the program this fall. Investors are looking for any hint on whether officials are growing more anxious to start to reverse their monetary accommodation.
* S&P 500 e-mini futures rose 4.75 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average e-mini futures gained 37 points and Nasdaq 100 e-mini futures rose 13 points.
* The S&P 500 has slipped 0.9 percent over the past three sessions, and on Tuesday it closed below its 14-day moving average for the first time since July 17. That level had served as support of late, and staying decisively below it would be a sign that near-term momentum is weakening.
* While this earnings season has been positive in aggregate, with more companies than usual beating expectations for both earnings and revenue, there have been some high-profile disappointments that worry investors about the state of the economy. On Tuesday, UPS gave a weak outlook that weighed on the broader markets, and last week Amazon.com Inc and Boeing Co disappointed. (Editing by Bernadette Baum)