Local mobile search and advertising network xAd today announced $4 million in expansion round funding as it attempts to maintain its 20 percent per month growth rate and conquer markets nationwide.

xAd said it will use the funds to expand its technology platform, scale its management team and increase its footprint in the local mobile advertising sector. Founded in 2001 by Dipanshu Sharma, the company has long said it aims to be the “AdMob of Local,” by creating a scalable local mobile advertising platform.

In an ideal xAd scenario, a potential consumer is walking down the street, doing a search on his phone. xAd sees what he’s searching for, knows where he is, and knows his past click-through behavior. Based on all of that, it delivers him the most appropriate ad from its network. The promise to advertisers is that, with xAd, they’re getting the highest possible click-through for their ad.

Achieving this goal has not been easy, nor even remotely quick: The company has only been profitable for close to a year, despite being the nation’s largest network of its kind with more than one million local and national performance-based advertisers.

But xAd says it has now begun moving steadily further into the black, after revamping its mobile search algorithms and creating in-house technology that identifies who, what and where an end user is.

“This additional funding . . . comes at the right time, while the local mobile advertising market is poised for growth. This new capital will help [us] better monetize the existing 10 million calls xAD generates monthly,” Sharma told VentureBeat today.

The current funding comes from venture capital firm Emergence Capital Partners. Jason Green, partner of Emergence Capital, will join the company’s board of directors.

San Mateo,Calif.-based Emergence is well known for its early involvement in other tech companies including aQuantive (which was acquired by Microsoft for $6 billion in May 2007), Doubleclick and Salesforce.

The VC firm says it now hopes to tap the local mobile sector of advertising, which is currently estimated to be worth $213 million but predicted to exceed more than $2 billion by 2014, according to local media consultancy the Kelsey Group.

“We have been waiting for the opportunity to invest behind a leader in local mobile advertising, the fastest growing segment of digital media today, and we found it with xAD,” Green said.