I'm referring mostly to Facebook as I expect most of my users will register with my wordpress site with that service but in reality the question could work with any number of other services...
Is is possible when a person leaves a comment on a post that it posts the comment made as a status update to Facebook/Twitter or Google + at the same time?
My interest here obviously is to get the person's friends involved in the comment thread...
You can have a look at our social sharing plugin for Wordpress.
It does not post automatically, as this require user intervention to post.
We might have misunderstood your question, and forgot to point out that although this is not provided by default, you can add it to do what you describe, by calling the sharing API endpoints.
docs.oneall.com/api/resources/social-sharing/, and https://github.com/oneall/php-sdk/blob/master/lib/sharing_message_api/publish_message_for_user.php for an example.