Social media spending will increase to nearly 21 percent of marketing budgets in the next five years, according to a new survey released this week. In 2009, it was only 5.6 percent.

The findings from The CMO Survey, sponsored by the American Marketing Association, Deloitte and Duke University's Fuqua School of Business, suggest that companies view social as a promising platform to engage with customers, gather information and build brand recognition.

And why not? Social is among the most popular activities online. By 2018, the number of social users worldwide is expected to increase to 2.44 billion.

Facebook has the largest market share among social channels with nearly 1.6 billion monthly active users. However, other services like Instagram and Snapchat, continue to gain in popularity.

Still, measuring social media’s impact remains a challenge for marketers, and many companies aren’t investing the time to develop clear social media goals.

Of those surveyed, only 3.4 percent reported that social media contributed very highly to company performance; while 40 percent reported below average contribution.

Which social network are you on?