Console: Teleporting yourself to an NPC or vice versa
I dismissed Serana at some point to hire a steward for my house, and although she said she would by at catle Volkihar, I could not find her there at all. So I searched for a way to teleport myself to her location using the console, which turned out to be rather convoluted.
Here's the solution should anyone want to do something similar:
1) First off, you need the NPC's Reference ID (refId). This is not the base ID that you can see in the Construction Kit nor the one you get using the help actorName command, but the ID of the reference of the actor in your game.
2) In case of a follower gone rogue, you are best off loading a previous save when you still had the follower, opening the console and clicking on the npc - this will display its refId. For some NPCs you can find the refId online - note however that this will not always work, since the refIds also depend on load orders. Serana's refId is usually 03002B74.
3) Once you have the refId, type this in your console:
To move yourself to the NPCs location
moveto player XXXXX
To have the NPC teleported to your location instead.
WARNING: Do NOT use the "player.placeatme refId" command! This will create a copy of the NPC, which will almost always not be what you need.