New York — Foursquare announced on its blog Wednesday that the company has surpassed 500,000 merchant accounts, just two weeks after the company reached 10 million active users.

Foursquare is a location-based social networking site that allows GPS-enabled mobile users to “check-in” at different locations, an activity that many participating companies reward with acknowledgment or special deals.

On Thursday the company introduced their new notifications feature to Android first, despite Foursquare’s history with Apple’s iPhones. The new feature will enable Android users to see when their friends have signed-up for the service, checked-in to a location, commented on a check-in, and engage in other Foursquare activities.

TechCrunch asked co-founder Dennis Crowley about the new Android-first approach, and he said, “Android needs some early-access love! […] We worked hard as a company to make it so different products are paced differently on different clients — so it’s not always iPhone, Android, then BlackBerry.”

Android recently overtook Apple’s iOS as the most popular smartphone platform in the U.S., according to comScore.

Launched in March 2009, Foursquare has a strategic relationship with American Express and this year raised an additional $50 million in funding.

Related Links: (Foursquare Blog) (TechCrunch)