Data from S&P Dow Jones Indices shows that the gains in Amazon (>> Amazon.com, Inc.), Facebook (>> Facebook Inc), Google (>> Google Inc) and Netflix (>> Netflix, Inc.) account for more than 50 percent of the broad S&P 500's rise of just over 1 percent so far in 2015. Add in Apple (>> Apple Inc.), and those five companies account for nearly 60 percent of the year's gains, according to S&P index analyst Howard Silverblatt.

Internal measures show fewer stocks are driving the market's gains, something that has happened in the past when equities were nearing a peak. The year so far has been bifurcated between big winners and big losers, with 35 stocks in the S&P up at least 25 percent this year, and 28 down that much.

"It's not a matter of a rising tide lifting all boats," said Silverblatt. "It's every boat for themselves."

(Reporting by David Gaffen, Rodrigo Campos and Christine Chan; Editing by David Gregorio)

Stocks treated in this article : Apple Inc., Google Inc, Netflix, Inc., Facebook Inc, Amazon.com, Inc.