I an writing a book, and I cannot find any soul stealing creatures that still look human! I was wondering if you could give me any examples?
- This appears to be a folkloric belief that has gained significant traction in the era of modern horror fiction.
The wiki for Soul Eater mentions an introduction of this idea in the Iliad:
But when even Bellerophon came to be hated of all the gods, then verily he wandered alone over the Aleian plain, devouring his own soul, and shunning the paths of men
The wiki also traces the origin primarily to the Hausa people of Nigeria, and includes multiple academic references, chiefly:
Witchcraft, Sorcery, Rumors and Gossip. (Cambridge University Press, 2004)
"Black Stomachs, Beautiful Stones: Soul-Eating among Hausa in Niger." In: Modernity and Its Malcontents: Ritual and Power in Postcolonial Africa. (University of Chicago Press, 1993)
Noppera-bō is the closest candidate to your description of a 'soul stealing' mythological creature. However, note that it can be described as 'face stealing' not 'soul stealing'.
Noppera-bō is a Japanese 'face less' Yokai (spirit), which looks like a human with just a plain sheet of featureless skin on their faces (no mouth or nose etc). It is believed in Japanese mythology that even though the Noppera-bō can disguise themselves as humans to 'scare' them, they are actually harmless, often disguising themselves as their target's face.
On the other hand, we can link a Noppera-bō as a depiction of the Face-Stealing Koh in the Avatar series. However, over there Koh is a shown as an evil spirit who steals faces of anything (human or animal) which expresses any sort of emotion in front of him. Thus to survive, one has to stay expressionless in front of Koh. If not done so he steals the face of his target and the victim will not die but remain faceless, eventually entering a state between 'life and death'. Moreover, Koh is shown as a large insect in these series with several pointed legs like a beetle, rather than a human.
Other shapeshifters linked to a Noppera-bō can be a Kitsune (Japanese fox) or a Mujina (raccoon dog), known to deceive humans. (If that is any use to you).
The second most closest candidate to your description could be the Sluaghs according to Celtic Folklore. In Irish, sluagh means 'host'. They were the spirits of the restless dead - so evil they were even banned from hell, therefore, they just roamed around in groups, coming from the West, to try to enter a house where a person had just died, to steal their souls. They either appeared as flocks of birds(ravens) or beasts, hunting for the weak or sickly people who were to die soon, waiting to devour their souls.
Lewis Spence writes in 'The Magic Arts in Celtic Britain';
"In the Western Isles of Scotland the Sluagh, or fairy host, was regarded as composed of the souls of the dead flying through the air, and the feast of the dead at Hallowe'en was likewise the festival of the fairies."