If you want to increase activity in your community, who should you focus on?
It's not your most active members. They're usually as active as they're likely to be.
It's not your least active members/lurkers. They're the hardest to convert into regular active members.
It's the people in-between.
Let's divide your members into four categories by the number of posts they make per month.
For example; tier one members post 75 - 100 times per month, tier two post 50 - 74 times per month, tier three post 25 - 49 posts per month, tier four post 0 - 24 times per month.
Focus on the tier two and three members. These are members that already participate, but not as much as they could.
You can deliberately segment these groups and develop clear, measurable, campaigns increase higher levels of activity amongst this group. This usually means engaging them in the community's sense of community elements (membership, influence, needs-alignment, or shared emotional connection).
Many organizations focus on their best or worst members, this is a mistake. Focus on the mid-level members.