Sometimes it can happen that either your Facebook or your GameCenter or both friends do not appear in the neighbour map.
The first thing to do then is to check if your Internet connection is working correctly, if it is, close and open the Smurfs App or log out and then in again into the affected service (i.e. GameCenter or Facebook). This should help most of the time and the friends should reappear.
Some users have also reported that if you try to connect to Facebook via your phone number instead of your email address the friends do not show up, but when they log into Facebook with the email address everything is fine, so please make sure you are logging in with your email.
If it does not help it can also be a server issue, for example if the developers of the game are doing maintenance. In that case just wait a couple of hours or a day and then the neighbours automatically reappear.
For Android Users: It has been reported that only the first 20 Facebook Friends (sorted by Facebook ID) are checked by that game as neighbours. If they do not play Smurf’s Village, than they do not show up. Beeline has been informed about this issue and should be able to fix it with one of the coming updates.
Important: Your friends are never lost, as long as they have not been unfriended in GameCenter or Facebook. As long as they are your friends in those services, they will eventually reappear and are not deleted.