I'm new, and I have a continuing entry in this Wiki that is being added to when I get update from somewhere else. Is there anything I need to do to make sure people who are interested in it are notified that an update has been added?
Typically, anyone who has ever made a comment or edit to the story will get an update. Also, depending on certain comments -- one's that may show favor to your story -- you can simply let them know on their talk pages.
However, I suggest creating a blog with a link to the story. That way when you add a sequel, you can simply update the blog. This allows you to not only keep people who have read your story in the loop but it also gives it a chance to reach a broader audience who has not.