US STOCKS-Wall St up on GDP data; Twitter has biggest jump ever

* Twitter (Xetra: A1W6XZ - news) rallies after blockbuster results

* GDP shows more economic growth than expected in Q2

* Fed statement awaited, expected to trim monthly stimulus

* Biotechs rally on Amgen (Xetra: 867900 - news) results, Regeneron trial data

* Indexes up: Dow 0.3 pct, S&P 0.4 pct, Nasdaq 0.7 pct (Updates to market open, adds analyst comment and Amgen results)

By Ryan Vlastelica

NEW YORK, July 30 (Reuters) - U.S. stocks were boosted Wednesday by some bullish earnings and a read on second-quarter economic growth that came in much stronger than expected, overshadowing a weak report on the labor market.

Gross domestic product grew at a 4 percent annual rate in the second quarter, above the 3 percent rate that had been expected and a sharp reversal from the weather-impacted first quarter, when the economy contracted a revised 2.1 percent.

Twitter Inc surged on heavy volume, jumping 25 percent to $48.25 in its biggest one-day advance ever after reporting that monthly active users had risen a better-than-expected 24 percent in the second quarter. The social networking company also gave a revenue forecast above forecasts.

"It all looks good today. Earnings have been decent and the GDP number surprised everybody for sure. In this rate environment, the market isn't expensive and we're still finding good values," said Gary Bradshaw, portfolio manager at Hodges Capital Management in Dallas.

Market participants shrugged off the ADP National Employment Report, which showed companies hired 218,000 workers in July, a level that was below analysts' projections and was also down from June.

The results bolstered support for Internet and other social media stocks, assuaging concerns the group is overpriced. Facebook Inc (NasdaqGS: FB - news) , which also posted strong results this quarter, rose 1 percent to $74.48. LinkedIn Corp rose 2.4 percent to $185.

The Dow Jones industrial average rose 51.8 points or 0.31 percent, to 16,963.91, the S&P 500 gained 8.01 points or 0.41 percent, to 1,977.96 and the Nasdaq Composite added 32.75 points or 0.74 percent, to 4,475.45.

The Nasdaq was boosted by biotechnology stocks for a second straight day. The Nasdaq biotech index was up 1.8 percent after Amgen Inc posted better-than-expected earnings and raised its outlook, sending shares up 6 percent to $130.67.

Also lifting biotechs was Regeneron Pharmaceuticals Inc (NasdaqGS: REGN - news) , up 9.8 percent to $334.46, after reporting positive results from a Phase III trial.

Among other results, American Express Co late Tuesday reported adjusted earnings in line with expectations, while WellPoint Inc (NYSE: WLP - news) beat expectations.

Shares (Frankfurt: DI6.F - news) of AmEx, a Dow component, fell 0.3 percent to $91.41 while WellPoint fell 2.7 percent to $109.55.

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 from UPS and Amazon.com Inc.

Later on Wednesday, the Federal Open Market Committee will release a statement as it concludes its latest policy meeting.

The central bank is widely expected to trim 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. (Editing by Bernadette Baum and Nick Zieminski)