There is a social order within every community.
If that social order is rigid, if it’s hard to move from being a member to being a top member, if the boundaries are impermeable (or appear so), members will participate less.
Or worse, social identity theory would predict they would attack members on the fringe of the group (perhaps newcomers) or out-groups to increase the feeling within the group.
It’s dangerous to have an accepted group of top members which never changes. Others will also feel the outsiders. If you always focus content, discussions, and other activities on the same group of regulars – members perceive it impossible to reach the same status.
It’s better then, to highlight the contributions of people rapidly rising within that community. Highlight the contributions of members whom have joined within the previous six months and have made a series of great contributions.
Offline, status is a subtle manner. We take both non-verbal and verbal cues. Online, you need to be more explicit. You may specifically state that this member is rapidly becoming a top member of the community. You can also specifically point to the contributions that have increased their standing within the community.
If you want more activity. Make sure that 1) group boundaries are permeable. People can increase their status and 2) they have a proven path for increasing their status. This is a path that has been taken by other members.