I don't know if this should be a thing that the site as a whole does or the party administrators. Looking at the party forums you can see that very few are active in the various forums/discussions.

This is a good suggestion, but we need more suggetions!

Maybe Party-specific High Score Boards for games could be one thing.

Something like Team Games, where all the Party have to work for a specific task with a prize at the end?

It'll encourage people to join and be active.

Support, I think their should be activities that you can only do in parties.

What type of activities, though?

This is something I've been thinking of for a while, I just haven't been able to come up with any ideas. 

You guys should all throw lots of suggestions out here! =)

I don't know erm maybe like a Team Scavanger Hunt?

I think Xee's suggestion is good.

Maybe even have a sort of "tug-o-war" thing going on that involves participating in activities ont the site? Like forum posting, playing games and quests... the more you play, the more rope on your side of the line your team gets.

*idea throwing* xD