Cullen missing in Skyhold

He's probably in another location.  He, and other characters, go to talk to other NPCs from time to time.  Go scouring throughout Skyhold (Maybe try Cassandra's location) to find him and eventually you should locate him.

I've been everywhere in Skyhold, and he's nowhere to be found ... even more so, if you have a quest to turn in, it should point into wherever he is, and its pointing to his office, so dunno.

This happened because you probably completed Sera's pranks before you picked personal Cullen's quest. This soldier in the tower should inform you that Cullen went to speak with Cassandra. But now she is inactive. Unfortunately I have the same problem, and I don't know how to fix it exept to load the save before you started a prank mission. 

 Simply save and reload then the charater appears, that works for me whenever a charater disapears.

I'm not Original Poster, but I have done this multiple times, Cullen is the only NPC that doesn't reappear. There is an "invisible wall" where he should stand, so he's there, but can not be seen or interacted with.

First time this happened, was in Haven (reappeared after 3-4 main quests quest where he relocated from out front chantry, to training camp) and now in Skyhold, too.

i did the mistake of not wanting to talk to him RIGHT after the cutscene interduced him

so i went to the hinterlands first and when i came back he wasn't there anymore. 

icon is on the map

there is an invisible wall where he should be

mashing V (on PC) didn't work.

traveling back and fourth to other locations in the war-room doesn't work

he IS at the wartable and their cutscenes!

and sadly no. he's not just "away on a mission" 

scouted whole skyhold for 2 days now.

he's just gone.

i spent like 6 of my 7 levels in hinterlands so i don't want to reload from then.

can anyone tell me how to fix it?

Reloading doesn't always work (in fact, has never worked for me). I've actually had the opposite happen. He's there and you save in front of him, then reload and he's 'gone' (or rather, present but invisible). Go back to a previous save to try again and he's there, but disappears again as soon as you save or go somewhere else.

It's a common bug. For me it's Varric, Iron Bull, Cole and Leliana who go missing. I leave the room and return, and that usually loads them.

This is definitely a bug, and definitely in Skyhold - absolutely bugged by Sera's pranks, not moved somewhere else, or temporarily invisible. It has happened in both playthroughs of mine but I didn't realize why he had disappeared until the second playthrough and I finally started looking online to figure it out. All the restarts in the world won't fix it.  I'm too far beyond reloading saves to get him back to talk to before the Sear pranks scene. The messenger just stands in the office completely uninteractable. Please fix this or just introduce a way to reset the messenger if it got interuppted with Seras scenes.