You have to have a competition that will keep them around for longer and always keep them interested. Switch it up some.
What you need is a revolving competition for the forums where the person can potentially earn rubies, ships, resources, etc...
Switch it up and people will stick around longer, its like a bribe to the players for being active in the forums. Like make the rule that the player has to of had an account for at least a month in the forums and must post at least twice a day for a week or something along those lines. (I am sure others will help out on this one)
As for in game, some people want prizes for being the best raiders or growers or blah, blah, blah. Simple, give out rubies for the top 5 position of each area or give area specific prizes. For example... If you come in first place for raiders of the week, every player gets 10 elite cargos, second place gets 8, third gets 6 and so on.
Top alliance of the week get a bonus for one week of all production.
People if you can, add on.
