Reconnecting Linkedin > http://en.support.wordpress.com/publicize/#reconnecting-linkedin

Manually posting to any social networking site is advantageous. Most of us are annoyed by auto-posted duplicated content that's spammed throughout social networks every time a post is published. It's impersonal and doesn't compel one to click in and read at all. Many bloggers have been bulk unfollowing others on social media and social networking sites as they are suffering from digital overwhelm. That's why manually posting unique snippets is now becoming a more effective way of promoting blog posts.

In July LinkedIn and Twitter, announced an end to their partnership that allowed users to sync updates from the two sites.
Also note Google plus does not provide an app for auto-posting.