If you use the Google Authenticator app from Google as a resource for 2 Step Verification, you may have problems or discover that your accounts don’t appear in the app. That’s because Google released a new version of the app in 2013 that has a flaw in the code. If users have this version, you’ll find that the app has been updated several more times since this was version was published I’m 2013.
In this article by Google, the problem is discussed in more detail, and solutions are offered. There are links for further help and assistance too.
Google Authenticator’s features vary somewhat by device type. You can find out about many of the features for various mobile platforms including Android, ios and Blackberry here. From this page you’ll find links to more specific information by platform.