Facebook Says, Lower Your Expectations About Mobile Here an ad, there an ad, everywhere an ad ad. Except on Facebook's mobile app, that is. Facebook amended its public offering prospectus on Wednesday to note that it is showing fewer ads per user on the site because of its lack of mobile advertising. It is the sixth amendment to the document since Facebook filed for an initial public offering in February. It said: In March 2012, we began to include sponsored stories in users" mobile News Feeds. However, we do not currently directly generate any meaningful revenue from the use of Facebook mobile products, and our ability to do so successfully is unproven. We believe this increased usage of Facebook on mobile devices has contributed to the recent trend of our daily active users (DAUs) increasing more rapidly than the increase in the number of ads delivered. The company also warned that if Facebook users continued to gain access to the social network on mobile devices, instead of computers, and if Facebook was "unable to successfully implement monetization strategies for our mobile users," the company's revenue growth could be harmed. Mobile is clearly a huge challenge for Facebook, and something the company sees as its future. The company mentions the word "mobile" 171 times in the prospectus. But it has also acknowledged the difficulties it may face while trying to build a meaningful advertising business on smartphones. The company went into more details in the update about its challenges in delivering advertising to the Facebook users who are getting access to the site on a daily basis. This segment of active Facebook users is continuing to grow quicker than the company's ability to show meaningful advertising, or sponsored content. Citing the number of ads shown to users, Facebook said in the amended filing: "We believe this trend is driven in part by increased usage of Facebook on mobile devices where we have only recently begun showing an immaterial number of sponsored stories in News Feed, and in part due to certain pages having fewer ads per page as a result of product decisions." Facebook has said 488 million people obtained access to the company's site through mobile devices in March.