tristan walker

As check-in champion Foursquare prepares to make a run at making money, the startup’s vice president of business development, Tristan Walker, has checked out.

Walker, who holds an MBA from Stanford and was once an intern at Twitter, announced his resignation from Foursquare in a blog post this morning. Walker is heading to Silicon Valley’s youngest elite venture capital firm Andreessen Horowitz where he’ll serve as an entrepreneur-in-residence. Holger Luedorf now heads up Foursquare’s business development initiatives.

“The opportunity at foursquare enabled me to think big, take risks, re-imagine what’s possible … and following an incredible journey, I have decided to resign from foursquare to pursue my next big dream,” Walker said.

Walker developed Foursquare’s significant brand relationships and was the mastermind behind the startup’s most progressive initiatives, including a massive loyalty campaign with American Express.

“There’s no better place for him to land than this entrepreneur in residence role at Andreessen Horowitz,” Foursquare co-founder and CEO Dennis Crowley told VentureBeat. “Tristan’s big thinking and drive have been invaluable assets to foursquare over the last few years. His work has helped solidify foursquare as a strong marketing tool for brands and a data-driven loyalty platform for merchants,” a company spokesperson added.

The exit could be perceived as a blow to Foursquare, especially as it prepares to take its first stab at a real monetization strategy with an ad platform slated for launch this summer, according to a recent AdAge report. VentureBeat has independently confirmed with multiple sources that Foursquare plans to test an ad platform powered by its Explore engine.

Couple Walker’s resignation with the recent ouster of co-founder Naveen Selvadurai and what you have are company growing pains visible for the world to see.

Why might there be trouble? Foursquare, as VentureBeat has previously reported, is a company in flux. Known primarily as a check-in service, the startup is battling a self-imposed identify crisis and hoping to prove to people, and soon advertisers, that its offering spans beyond the tiny little niche of check-in apps — just 6 percent of online adults use geolocation apps — and is in fact a tool for real-world discovery.

Foursquare is also no longer the industry’s darling up-and-coming mobile app, despite recently surpassing 20 million users. Instagram, Pinterest, Viddy, and others have stolen the company’s thunder; they are the new hotter-than-hot services web denizens and press are salivating over. And nearly a year after raising $50 million in a round led by Andreessen Horowitz, Foursquare has yet to prove that it’s worth a $600 million valuation.

But don’t read too much into the high profile departures, they’re nothing more than normal exits for a three year-old startup still finding its way, Crowley said. Crowley referred to Foursquare’s current operations as “organized chaos.” With a 115 people on staff, Foursquare is brewing the next PayPal mafia, he said, meaning that he fully expects a handful of staffers to leave and build their own companies.

“We’re a machine now … Foursquare is a completely different place than it was a couple of years ago,” Crowley said. “Everyone here is bullish on the direction of the company.”

Walker could not be reached for comment.

Photo credit: Mari Sheibley/ Flickr. Used with permission.