There is no FTP access top free hosted WordPress.com blogs and we blogger cannot install any plugins at all. Plugins are for WordPress.ORG installs only.
You can use RSS Grafitti http://www.facebook.com/RSS.Graffiti for posting to Facebook walls if you prefer. RSS Graffiti periodically checks the RSS/Atom feeds that you specify and posts any new entries it finds to the Facebook Walls that you specify. You can get any feed written on any wall (Facebook Profiles, Fan Pages, Groups, Events and Application Profile Pages). In fact, multiple feeds to multiple walls. You choose the combination.
As for other methods for posting to other sites like Twitter clients, etc. you will have to use Google search.