many others are almost doing nothing, due to low board activity like those in some local boards.
...
how to complaint about him?
So you seem to pointing to someone here?

Absolutely Not. I don't have any complaints against any mod.
Also, is participation in the discussion one of the moderator's tasks?
It's not, so what to do when to asking about some improvement for a local board (add and move pinned topics/adding sub-boards/setting local rules for the boards...) when the mod doesn't participate in discussions?