No, the correct form would be "Among the crowd were vampires".
Since there are multiple vampires (or a plural noun), "were" should be used instead.
One tip that usually works is to switch the subject and object of the sentence around and *read it out loud*. If it doesn't sound right, it's probably not right.
"Among the crowd was vampires." to "Vampires was among the crowd".
"Among the crowd were vampires." to "Vampires were among the crowd."
The second pair of sentences sounds better, right? It's not always correct, but this can help you out.