Storyteller is quite useful in Pathfinder: Wrath of the Righteous, which is probably why you're trying to find him in the city, even though he's not necessarily there.
Taking Drezen from the demons busted Pathfinder: Wrath of the Righteous wide open with brand new activities for the players and a new chapter to adventure through. However, all those friendly NPCs you've come to rely on might be in different positions and Storyteller really took this game of hide and seek to heart.
The reason why you can't find him in Drezen is that he is not immediately present in the city. You will first need to complete the quest The Dragon Hunt. It will first instruct you to go to the tavern and hire Greybor and after that point, you will be tracking the extremely dangerous beast across several locations.
It is only after you reach Artisan's Tower that you need to pay attention. Spoilers for the quest will happen in the next few paragraphs so read at you own discretion.
You will find Storyteller by taking the stairs next to the golden mechanism on the floor. Talk to him and he will ask you to help him with finding Elven Notes again. You can loot nearby bookshelves to find one piece and eventually return it to the ancient elf.
After the first phase of the fight with the dragon, she will take off and you will need to chase her to the second floor as soon as possible. You're on a timer here so make sure you catch her as soon as possible to finish the beast off once and for all, before she burns the Storyteller's books.
Once you're done with all that mess, Storyteller will move to Drezen and you will be able to find him next to the Citadel entrance in the city. He will also have a purple marker on the map so he won't be hard to find anymore.