Foursquare said Friday it had received $50 million in venture-capital financing from Andreessen-Horowitz, Spark Capital and existing investors O’Reilly AlphaTech Ventures and Union Square Ventures.

The check-in service plans to use the funding to hire more engineers, add new products targeted at small business owners and expand into international markets.

“Having our current investors double down on us is a tremendous gesture of support for foursquare and for the direction we’re headed,” Foursquare co-founders Dennis Crowley and Naveen Selvadurai said in a post on the company’s blog. “The opportunity to build something meaningful in the location space is HUGE, and we feel well-positioned to capitalize on it.”

More than 10 million people are currently signed up for Foursquare, up from just 1 million in March 2010. The company has also expanded its workforce over the past year and now has more than 70 employees, up from just 15 in 2010.

Foursquare is working to come up with ways to bring in revenue through its app, which is free to consumers. Last week, the company announced a deal with American Express that allowed customers to get exclusive discounts when they used their credit card at venues signed up to Foursquare’s service.