Sometimes, the best way to attract new customers is by tapping into your existing ones.

Extole, a referral marketing company that helps you turn your customers into brand advocates, announced today that it has raised $5 million in funding from Norwest Ventures, Shata Ventures, Redpoint Ventures, and Trident Capital.

The company says it has grown its customer base by 85 percent over the past year, adding the likes of Forbes, GrubHub Seamless, and The Economist. Extole has also powered more than 400 referral marketing campaigns.

“Marketers shouldn’t have to make a choice between acquisition and advocacy. They have the right to reward their own customers for their support, not just write checks to Google,” Extole CEO Matt Roche said in a statement.