What do you call a person who collects pens?

Answer 1

PENOPHILE

a person who collects pens. Need not be fancy pens and includes those who inadvertantly pick up other person's pens and forget to return them. Generally has a stash of a wide variety of types of pens in drawers, coffee mugs and the bottom of the washer.

Andrew, being a penophile, adroitly picked up the server's pen, signed his check, then pocketed the pen to add to his collection.

http://www.urbandictionary.com/define.php?term=Penophile&defid=3893725

Answer 2

They are pen collectors. They have organizations.