There are a lot of tools that PR functions can use to monitor social media.
But the New York Times points out collecting what a company posts on various social media platforms can be difficult. You can search on Twitter or on your blog post or Facebook, but none of the current tools are 100% accurate. There are lots of times when Twitter can find recent posts, much less those going back a year or more.
The New York Times points out the problem in an article worth reading, "Tools to Help Companies Manage Their Social Media."