First of all social media is a subset of media. Certainly special considerations apply to social media, but it should be treated as an aspect to your overall media relations effort.
Start by identifying the reporters who cover your field. While it may sound counter intuitive, you should define your business as narrowly as possibly, at least for internal purposes. Your chances of placing a story will be greatly enhanced by sending it to the reporters who cover that precise beat.
Get familiar with the reporters before you send them a pitch. If you don't have time to do that and run your business, hire a professional. Getting familiar with reporters is easier than ever. Almost all technology reporters are on Twitter, follow them. Even if you are not inclined to Twitter, you should have an account for listening purposes.
If you are a small company, your chances of placing a story are more difficult that ever, With publishers cutting positions, the competition for remaining space is tougher than ever. On the other hand, you can just use a press release service to put your story out and at least it will be on the web to be picked up by search engines. You should also put it on your website, in html. For small news announcements, a blog post should suffice.
Blog posts should occur regularly, not necessarily often, but predictably. Refreshing content gives people a reason to return to your site. Again, if you don't have time to blog regularly, hire a professional.
Now the big question, to Facebook or not to Facebook, that is the question. At this time I would say not if you don't want to. For software companies Facebook is still optional. If you are selling directly to consumers, I encourage you to set up a Facebook page and regularly update its content. If you don't have time, or are not inclined, hire a professional.