Advertising agency group WPP has seen its market capitalization fall $2.6 billion after it reported flat results Thursday.

WPP's shares were down almost 13 percent and the firm's chief executive, Martin Sorrell, said there were several reasons for the lack of revenue growth.

"The major factors influencing this performance were probably the long-term impact of technological disruption and more the short-term focus of zero-based budgeters, activist investors and private equity than, we believe, the suggested disintermediation of agencies by Google and Facebook or digital competition from consultants," he said in an online statement.

Speaking to CNBC's Squawk Box on Thursday, Sorrell said 2017 was a difficult year and that WPP had to adapt in the face of disruption. "We have to simplify how we operate, we have to be faster and better and cheaper in a world which is obviously being disrupted by technological developments, whether you are talking about manufacturing, media or distribution, so we have to change the way we do things, simplify things," he said.

Rival agency groups are also suffering, with Omnicom reporting 2017 revenue down 0.9 percent while IPG had a sluggish 2017.