This is a major concept in my Keeper's of Dylann series. Brainstorming with Leah today I got most of it worked out. What I really need right now is some good names. I like wraiths but the others are just... random. In a not good way.
The Darkness
The darkness is a malevolent presence. It is, it surrounds you, it overwhelms you. It feeds off of fear. It is not telepathic however, it must convince you to reveal your fear. Sometimes it does this through its presence, or by leading you to the things you're afraid of, but occasionally it will resort to talking to you. Not directly, of course, just leading you out; getting you to talk.
Once the Darkness has taken hold of your fear it drains you, leaving you a wraith.
Wraiths
Wraiths are sort of like a soul without a body. They're people with no physical form. Your consciousness with no sense of heat, cold, pain, pleasure, hunger, etc.
All a wraith can do is think, speak, and weep. Even their sight is blurry and dim, like seeing shadows.
Invisible Ones
(this is the name I like the least)
Invisible Ones are evil wraiths. They are the ones who, when consumed by the Darkness, become consumed with it. They take pleasure in the sufferings of others. Their only goal is to turn as many beings into invisible ones like themselves. They serve the Great Darkness.
**
Well, any questions? Name suggestions? Thoughts? Suggestions? Have at 'em.
Creepy... (in a good way. 
)