By Alexei Oreskovic SAN FRANCISCO (Reuters) – Facebook Inc said on Wednesday that it is displaying ads from a small group of marketers on other companies smartphone apps, the latest sign that the worlds No. 1 online social network is closer to launching an ad network business. Facebook said that the test is currently limited to a few advertisers and mobile app publishers. Our aim is to demonstrate even greater reach with the same power of Facebook targeting for advertisers both on and off Facebook, the company said in a post on its official business blog. Facebook generates the bulk of its revenue from ads that appear on its own pages and in the Facebook mobile app.