Why is he experimenting on vampires?
Also, unless he gets hold of Forest or one of our characters, I don't think most of the PCs are going to care about a bunch of vampires going missing. They're not our friends, and the vampires in general don't have a good reputation here. Experimenting on and torturing them is a bit much, yes, but kidnapping them in itself isn't a massive issue unless the vampire being kidnapped is known to the main characters, because the main characters so far have seen little indication that most vampires are anything other than evil.
Sakura would be a little wary of such a broad designation (as would be Rider, but she couldn't give a fuck because Sakura isn't a vampire and nor is any of her family), but I doubt they're going to be bothered enough to risk their lives looking into it given that vampires are mostly ruled by Frost, who is a dick.