US STOCKS-Wall St set to extend selloff

* Amazon jumps after posting unexpected profit

* Visa (Xetra: A0NC7B - news) rises after results beat expectations

* Biogen (NasdaqGS: BIIB - news) slumps after slashing forecast

* Futures: Dow down 31 pts, S&P down 2 pts, Nasdaq up 3 pts (Adds details, comment, updates prices)

By Tanya Agrawal

July 24 (Reuters) - Wall Street was set to open slightly lower on Friday with major indexes poised to end the week lower amid a mixed bag of earnings from big companies and the downward spiral of commodity prices.

Amazon.com (NasdaqGS: AMZN - news) shares jumped 21.5 percent to $585.64 in premarket trading, a day after the online retailer posted an unexpected quarterly profit.

Dow component Visa was up 6.3 percent at $76.29 after the credit and debit card company's results handsomely beat expectations.

Starbucks (Swiss: SBUX.SW - news) rose 4.8 percent to $59.26 after the world's biggest coffee chain reported a higher quarterly profit.

S&P 500 e-minis were down 2 points, or 0.1 percent, with 121,593 contracts traded at 9:04 a.m. ET. Nasdaq 100 e-minis were up 2.75 points, or 0.06 percent, on volume of 23,010 contracts and Dow e-minis were down 31 points, or 0.18 percent, with 14,940 contracts changing hands.

U.S. stocks ended lower on Thursday, with the blue-chip Dow Jones industrial average slipping back into the red for the year, after disappointing corporate results and forecasts added to concerns about the U.S. profit outlook.

Second-quarter S&P 500 earnings have been mixed, with 75 percent of companies so far beating analysts' profit expectations but just 52 percent surpassing revenue expectations, according to Thomson Reuters (Dusseldorf: TOC.DU - news) data.

RBC Capital Markets said investors were treating disappointing stocks harshly. While only 20 percent of companies have missed expectations, below the 23 percent over the past three years, there was a 3.5 percent selloff versus the 2.4 percent seen historically, a note said.

Adding to the concerns regarding lukewarm earnings, the S&P 500 is relatively expensive, trading at 16.9 times forward 12 months' earnings, above the 10-year median of 14.7 times, according to StarMine data.

"We still need to see more earnings to get some clarity on how this earnings season is going to turn out," said Adam Sarhan, chief executive of Sarhan Capital in New York.

"Investors are concerned about a lack of revenue growth and with the transport index being in correction territory and commodities selling off, there is a concern that the global economy isn't strong enough."

Metal prices hit multi-year lows on Friday as weaker-than-expected data from China and the euro zone raised concerns about global growth while oil prices neared four-month lows.

Investors will continue to focus on earnings report with nearly half of the S&P 500 companies having reported results.

Biogen slumped 12.4 percent to $337 after the biotechnology company's forecast came in below consensus.

American Airlines (Xetra: A1G.DE - news) rose 2.6 percent to $43.68 after the company's quarterly profit beat estimates.

Data expected of Friday includes new single-family home sales for June, which is likely to remain steady at 0.546 million units. The data is expected at 10 a.m. ET (1400 GMT).

Financial data firm Markit (NasdaqGS: MRKT - news) 's preliminary Manufacturing Purchasing Managers' Index for July is expected to be unchanged at 53.6. The numbers are expected at 9:45 a.m. ET. (Editing by Don Sebastian)