Thom's book on Beginning Kentico Development covers this exact example except I could not get it to contact Twitter. But you might be able to get Thom to show ya how to get it up and running. I am sure it is a small fix. Here is the link to his
book.
In the book you actually create a twitter alert every time a blog post is created. Using the Global Event Handler sample as the basis. I am sure you could use the same to post content to Facebook as well.