ShareThis today announced a new tool that will allow publishers to turn their sites into social readers without having to build their own custom Facebook applications.

ShareThis is known for creating widgets that are used across more than 1.4 million websites to make it easy visitors to share content to their social networks. With the new ShareNow feature, publishers can take advantage of Facebook Open Graph and give visitors the option to automatically share their reading activity back to Facebook. This could lead more blogs and media sites to add social reader functionality that could drive additional traffic and awareness for their content. At the same time, Facebook will benefit from the additional data that can then be used to target ads.

When users visit a page with ShareNow, they have the option to login with Facebook and grant the app permission to post to Timeline. The widget remains present when users scroll down the page. Users can easily turn automatic sharing on and off, or remove activity that they didn’t mean to share. Once users authorize the app on one site, they do not have to re-add the app when they visit another site also using ShareNow. However, by default, the widget will be disabled on all other sites until users switch sharing to “on.”

The tool will be useful for publishers that aren’t experienced in Facebook app development. Facebook has its own social reader plugin called “Recommendations Bar” in beta that some sites like Mashable are testing. [Update 7/26/12 11:29 a.m. PT - Facebook has brought Recommendations Bar out of beta, but it no longer shares users' reading activity, so it is not competitive with ShareNow.]