Investors should continue to look to e-commerce companies for investment opportunities. E-commerce sales grew steadily in 2014, comprising 6.6 percent of total retail sales in the third quarter, up from 6.4 percent in the second quarter and 6.2 percent in the first quarter, according to data from the U.S. Census Bureau.

Several private equity firms made significant e-commerce investments in 2014. In October, New York private equity firm Siris agreed to buy e-commerce services provider Digital River (Nasdaq: DRIV) for $840 million, as the lead buyer in an investor group. The deal is expected to close in the first quarter of 2015. The target provides e-commerce services to clients that include HarperCollins Publishers, Mattel Inc. (Nasdaq: MAT) and Spotify.

In another PE take-private transaction, Chicago private equity firm Sterling closed a $109 million deal for Innotrac Corp. in January. Innotrac provides digital technology integration, fulfillment and contact-center services to global brands, including J Crew.

PE firm Tritium Partners and StepStone Group agreed in August to buy a majority stake in e-commerce services provider Access Technology Solutions. The Provo, Utah-based target provides cross-border e-commerce services through cloud-based technology, serving about 75 merchants worldwide.

See the next trend in our special report: Private Equity will Drive More Fracking Deals