• It was "fair" that Facebook took time to look into the data misuse allegations surrounding Cambridge Analytica given how complex the issue was, said Martin Sorrell, CEO and founder of WPP.

• The social media giant was criticized for not responding quicker to those allegations and informing users of the alleged leak earlier.

• Google and Facebook must "step up to the mark" because they're not merely technology companies, Sorrell said.

It was "fair" that Facebook FB took time to look into the data misuse allegations surrounding consultancy Cambridge Analytica given how complex the issue was, the chief executive of the world's largest advertising group said Monday.

Martin Sorrell, CEO and founder of WPP WPP-GB , made those comments after the social media giant was criticized for not responding quicker to allegations and informing users of the alleged leak earlier.

"I think it was fair that they spent time looking at what exactly happened. It's quite complex the issue they're at," Sorrell told CNBC at the China Development Forum .

"Firstly, they've been misled so ... they're responding to that, trying to make sure it doesn't happen again. They're looking at all the possibilities," he added.

The issue of data privacy came under the limelight after Cambridge Analytica was said to have improperly obtained users' information from Facebook. The firm has said it helped elect United States President Donald Trump in 2016.

Recent opinion polls in some countries found that people are losing trust in the social media giant.

In general, technology companies such as Google GOOGL and Facebook must "step up to the mark" to take greater responsibility of their respective platforms, Sorrell said.

"With power comes responsibility. They have the resources. In essence, they're media companies, they can't say that they're technology companies not responsible for their content," he said. "They need to step up to the mark."

Sorrell said new media companies account for about 30 percent of worldwide advertising — Google and Facebook together make up 75 percent of that market share. Their sheer size means they're obligated, he said, to make sure users know how what they're getting themselves into.

"At the heart of this is about data and data privacy, and whether the consumers really know what he or she is letting themselves in for. When they opt in on those complex agreements you have to sign when you go on the site, you and I we just say agree and we accept without really knowing what we're letting ourselves into," said Sorrell.