Facebook has started testing a search engine within Facebook that will allow users to post links to content without having to search it from Google.

Some U.S. users will begin to see an "add link" option next to other buttons, after which the user will type a search term and links will appear.

"The addition of the in-app search feature aims to continue the centralization of mobile users' activity to its own platform," said IHS Technology senior analyst Eleni Marouli. "The more functions the Facebook app can deliver, the more user engagement it can provide for its clients: advertisers."

This is not the first time that Facebook has tried to enter the search game, with previous attempts drawing mixed response. In 2013 the company unveiled Graph Search in an attempt to help users go through the millions of posts being uploaded and typed out each year. Of course, the company also had a long partnership with Microsoft to bring Bing search results to searches conducted within Facebook. This relationship between the two companies ended last year.

The move is yet another attempt for the company to keep users inside the Facebook app and to cut down on how much it relies on other companies.

The emphasis on keeping mobile users within the Facebook app is not for no reason. Facebook recently reported that a massive 73 percent of all of its advertising revenue came from mobile devices. Not only that, but almost 9 out of 10 Facebook users access Facebook through a mobile device. Because of this, Facebook accounts for around 46.8 percent of mobile ad revenue.

Facebook also said that it has indexed a whopping 1 trillion posts, meaning that results found in Facebook are often of data that Google does not have.

Of course, Google won't be going down any time soon. While Facebook might start to chip away at Google's dominance a little, Google will remain the king of search for the foreseeable future.

"We're going to start off focusing on stuff that's unique to Facebook, that you couldn't really answer those questions elsewhere," said Mark Zuckerberg in a conference call in July, when discussing the indexing of data.

Facebook's "add link" program is still being tested, and it is not yet known how long it will be before the feature is rolled out to all mobile users. Currently it is only being tested on iPhone; however, it is likely that Facebook will also test the feature on other operating systems.