You live in a relatively small town and spotted a vampire, what do you do?
Typical horror movie set up. You see a vampire feed on someone and fly away with their body. You do a little research and learn disappearances happen more often than usual in your county, particularly for homeless or other less visible people. The point is there is absolutely no proof. But you know it is in the town you live in.
What do you do if anything? Or just move? And yeah, no one will believe you obviously without proof you don't have and likely can't get safely.
Edit. typical vampire powers. you have no idea how long it will stay, but safe to say if you do nothing a lot more people are likely to die. But of course you can just stay in at night. no obligations to really do anything.