According to the [rules for invisible creatures](http://www.d20pfsrd.com/gamemastering/special-abilities#TOC-Invisibility) and the [*invisibility* spell itself](http://www.d20pfsrd.com/magic/all-spells/i/invisibility), objects the creature picks up while invisible would remain visible unless they were tucked into a pouch or pocket (where you wouldn't normally be able to see them even if the creature were visible), so the arrow should at least mark the creature's square for you (you'll still suffer the miss chance for attacking an invisible creature, but won't have to guess the square).

Note that while you said you were fighting a demon, I'm thinking there's a decent chance it's actually an imp or zebub, both types of devils.  They're both small in size and have *invisibility* as an at-will power - so the creature can spend a single standard action to become invisible again on its next turn, and then a move action to move to a new square so you'll have no clue where it is again.