As part of the ways to improve members' participation, I suggest that you create:

Top Poster of the Week or Month

This can be chosen by using the number of 'likes' a post gets within the period under review. The top poster could be from a section or throughout the forum.

You may also consider using the number of 'dislikes' a post gets. However, in this case, the 'dislike' button needs to be added.

On another note, it would also be good to know the poster with the highest number of posts within a period. The downside of this is that it's not necessarily so much about quality but quantity.