Do psychic vampires exist? If so, what can we do to protect ourselves?

Yes, they do exist! Let's try for a definition first: Psychic vampires feed off the life force of other sentient beings.
Why would they do that? In my experience, the class of entities that feed off others are like parasites: they drain their host of life force energy, but may not even be fully aware of their acts. It is simply who they are, what they do. These entities are by nature parasitic, i.e. they need a host to support their own existence.

How do we attract psychic vampires?

When our auric field has been depleted by traumatic circumstance (illness, loss of a loved one, etc), we become more vulnerable to other beings. Also, in the case of accelerated personal evolution, the light we give off becomes more 'visible' to other beings. We are susceptible to become "food" for others that are lacking in life force energy and are looking for hosts to attach to. Many of these beings are not 'evil' by nature; they simply look for energy food as a means of survival.
What can we do to protect ourselves?