"Post more" (simply in the sense of "more posts") is indeed not what advertisers need.

What advertisers need is more readers, more potential customers for their services.

But what attracts new readers to the forum? Good content. So a type of supply (posts, thread) that can attract new readers is probably the only way to make advertisers get more interested in signature campaigns. In general thus I agree with @mindrust if "post more" means "post more quality content". Even better if it's "shareable" in social networks or so, to begin to attract people from other platforms here, as I wrote in my last post here.

Spam posts achieve exactly the opposite.