Scribd CEO Trip Adler is betting on the Facebook effect. His document-sharing startup is one of its launch partners for the company’s new Social Plugins, a group of features that will help web publishers take advantage of Facebook’s social graph to bring more users to their sites and keep them around longer.

Often dubbed the YouTube of publishing, Scribd lets users self-publish text from a master’s thesis to a novel. Most of the content is free. More than 10 million documents have been uploaded to the site so far, and 50 million people visit each month.

“Facebook’s tools create a new use case for Scribd,” explains founder Trip Adler. “Until now, it was about uploading documents, but now it about both publishing and reading.”

To cut through the jargon: These social steroids could increase user engagement significantly. Right now, Facebook is the site’s largest source of traffic after the major search engines, but it still only contributes a fraction of Scribd’s visitors. Adler is bullish that over time, Facebook’s new tools could make it a competitive traffic driver to Google.

Initially, Scribd will draw from Social Plugins to add two dynamic elements to the site experience. Scribd readers will be able to “like” what their favorite reading materials, using Facebooks new button. Using Facebook Connect, they’ve already been able to share books on Facebook, but this is different. Shared material is ephemeral, disappearing from news feeds quickly. When a reader likes a book, that action becomes a permanent part of the Facebook page.

Also, a small newsfeed box will offer a stream of updates about what Scribd readers are reading and make recommendations. This is the type of tool that keeps half of Facebook’s 400 million plus users returning to the site daily and causes them to spend time on the site.

Scribd is launching a product of its own today as well. Readcast will let readers share what they reading—and writing, downloading and commenting on—automatically with Twitter and Facebook. A pop-up menu allows users to opt-in permanently so every action on the site is shared.

Scribed appears to be laying the groundwork for a deeper integration with Facebook’s social graph. In time to come, that could make the company a conduit for larger publishers trying to socialize their content. Says Adler: “Let’s say Random House wants to share a book on Facebook. We become the place for Random House to get that content shared on Facebook. With like button, readcast and the activity feed, we become the best place for Random House to share that content.”

Just as search engine optimization delivered big returns to the companies that figured it out the earliest, this new form of social optimization will offer rewards to the first companies that figure out how best to take advantage of it. Let the games begin.