BranchOut, the largest professional networking service on Facebook with over 20 million users, has raised $18 million in a recent round of venture capital funding led by Redpoint Ventures. In September the company raised $6 million from several of Silicon Valley’s most prominent angel investors as well as Accel Partners, Norwest Venture Partners and Floodgate.

BranchOut, which has over 3 million job listings and 20,000 internship listings, also announced a new feature called Jobs Tab. The Jobs Tab allows companies to post their job listings to their Facebook Page and makes it easy for users to apply or share specific listings with friends on Facebook.

This service is particularly helpful for companies who have large followings on Facebook. Take a company like American Apparel for example, who posts all job listings on their website. Many people looking for jobs feel lost and stumble into the store to apply but never gain access to the top corporate positions because they don’t know they exist. This service will help companies spread their search through a platform most people have immediate access to. While LinkedIn is obviously the frontrunner in professional social networks, it hasn’t really integrated itself into Facebook like BranchOut.

Large companies like Levi’s, Groupon, Kiva, charity: water and Readyforce have already adopted BrachOut’s beta program as well as others.