Some plecos NEED to have some wood as part of their diet, others just like to have some to graze on.
All of them prefer to have some sort of hiding place. It can be a piece of driftwood, a rock cave or even a length of pipe. If there is no hiding places they will usually end up huddling nervously behind a filter intake or similar. If you provide more shelter the pleco will usually be less nervous and you will see it out in the tank more, rather than less.
Cheers
Ian