My understanding is that this will only work if a vampire breaks in on a family you are actively playing and drinks from them. Otherwise it's up to you to play a vampire and drink from other sims possibly turning them. I don't think it is possible for NPC vampires to autonomously drink from other NPC.
Though in saying that, I have noticed that making a club with the chosen activity being 'drink plasma', will cause unplayed vampires to drink from other sims if you are actively playing a sim where the club is gathering. You could try that and see if anything happens.