OK a guess on my part, buddy at camp girlfriend has 3 small dogs like your's
several times, she was outside at night with the dogs, and a dam owl almost got one, right in front of her, all 3 were off leash, the owl JUST missed, so after that she would never let them go out off a leash
her thinking was if the owl grabbed it on a leash she would pull it free
I think it would also mean it would gut the dog, they have big tallons
but many times she would eb outside wlking the dogs and see owls perched off in the dark in the moon light
so, my vote is for am owl
I also know for a fact people will pick up dogs , all the more so on small dogs, they see walking freely, thinking they are lost or??
if you don't live close to where a road is, where it could have been seen
I say an owl got it
as if a coyote got it you'd see there tracks, and they will eat a small dog too!, same as a fox, even a very hungry other small critter like a skunk, or a coon
this was bad winter, so most things would eat what they could get
and last
sorry for your loss
it sucks big time to loose a pet, lost mine 2+ yrs ago, and still miss him alot!