A private investigator and hunter of supernatural creatures is searching for a missing twenty-year-old woman when he stumbles upon a vampire coven with plans to enslave humanity.

It could be interesting, but we don't know. This logine seems to describe the first 25 pages, but doesn't give any info about the meat of the plot. How about this- "While searching for a missing teen, a paranormal investigator stumbles upon a vampire coven with plans to enslave humanity and..."

In loglines it helps to start with the event that triggers the story (Inciting incident)

"After a young girl goes missing..."

Also, if the story is personal in any way, it helps up the ante'

"After his sister goes missing..."

Hope that helped, good luck with this!

Paranormal investigator