In most other games I have played, you can look for specific players to battle. It creates competition, and excitement (and most important to the Dev's causes people to spend MORE money!). What is a PvP game where you are stuck with only randoms? Get a friend to play but can never find them to attack? Gets pretty boring. What did care if I get hit by someone I don't know, and can't even talk back to them? Rivalries, Challenges, bragging rights, etc... is what makes for fun PvP, and also makes a Forum like this one really come alive. Let me give some examples of a few other games: Game of War (has held Top App in Apple Store longer than any App): Players can locate other players by their coordinates, or just scanning the field for them. They also have in game chat rooms, and you can ask where people are, where to find revival alliances (Guilds here), etc.. Players taunt each other, challenge each other, and brag about great battles, etc all in the games world chat.. Kingdom Age (Did so well GREE bought it from Funzio): You attack players by searching through a list of names in your battle list, that refreshes for free. You also have personal walls attached to each Kingdom (Islands here), where you can post messages to that player. Their Game Forum is VERY active with players having a great time loving or hating each other, and posting about attacking each other. Guilds have forum relationships with other guilds and even work together attacking enemy Guilds. Racing Rivals (CIE Game, and their cash cow): Players go into a chat room for the server they are on (you can change servers, if you want by clicking next). Players talk on that servers chat room, and challenge each other to races for money, or even for pink slips to their cars (yes the loser really loses the car they built). I am sure someone will complain here that "oh no that might cause bullying, etc..." WELL this a Pirate (you know the terrorists of the Seas, read your History there was NOTHING nice about these guys) Game, and a PvP game. Not your speed? I heard Farmville is still being played somewhere. LOL ;-)
In games like this it sets up situations that can be exploited. 1) making other accounts strictly to use as farms for your main base. 2) farming lowbies for easy battles without suffering any PR loss 3) bullying, know that a guy has a certain setup base that you can walk through you could keep them from ever gaining resources. 4) etc Maybe a better idea, and one that has been suggested is being able to attack your fb friends and guild mates in friendly battles. Kind of a way of base testing or learning how to use your troops more effectively without the troop loss. Add a grog or gold cost to the battle or a cap to how many times a day might be a good thing as well.
Don't have facebook, and not getting one for a game. And the above that I posted was from other games, so seems to be working well.