Go to Northpoint (the town in the northeast corner of Rivenspire) and ride west along the shore past the fishing village. Ride over the bridge, turn left when the road splits near the lighthouse. There's a passage under a very large rock, ride through that. Keep riding west past a few ayleid ruins until you see a camp with friendly NPCs. You should find everyones favorite vampire there.

Found it thanks to you 2. I can't tell you how many times I rode from coast to coast trying to get there. Sometimes trying too hard is not an asset.