simplesite,
I've never used MyBlog before, but I believe there's an option in there to have it use Joomla Content plugins. If so, make sure that's enabled obviously. Then, the settings in the Social area of JFBConnect should work.
Again, I've never used MyBlog, but I believe we've heard that the answer above works for other users. If that doesn't work, let us know. We can try to look into it further. However, we don't have any built-in MyBlog support, so if the above doesn't work, I'm not sure how easy it would be to add it.
Thanks, and good luck,
Alex