In v2.0 of the Graph API, calling
/me/friends returns the person’s friends who also use the app.
In addition, in v2.0, you must request the
user_friends permission from each user.
user_friends is no longer included by default in every login. Each user must grant the
user_friends permission in order to appear in the response to
/me/friends. See the Facebook upgrade guide for more detailed information, or review the summary below.
If you want to access a list of non-app-using friends, there are two options:
If you want to let your people tag their friends in stories that they publish to Facebook using your App, you can use the
/me/taggable_friendsAPI. Use of this endpoint requires review by Facebook and should only be used for the case where you’re rendering a list of friends in order to let the user tag them in a post.
If your App is a Game AND your Game supports Facebook Canvas, you can use the
/me/invitable_friendsendpoint in order to render a custom invite dialog, then pass the tokens returned by this API to the standard Requests Dialog.
In other cases, apps are no longer able to retrieve the full list of a user’s friends (only those friends who have specifically authorized your app using the
user_friends permission). This has been confirmed by Facebook as ‘by design’.
For apps wanting allow people to invite friends to use an app, you can still use the Send Dialog on Web or the new Message Dialog on iOS and Android.
UPDATE: Facebook have published an FAQ on these changes here: https://developers.facebook.com/docs/apps/faq which explain all the options available to developers in order to invite friends etc.