Facemate
A facemate is someone you added on Facebook just to look cool, even if you don't know them. They're not friends. They're just people you pretend to know.
My gym instructor is my facemate. I don't even know his name.
I added my neighbor's dog on Facebook. Now it's my facemate.
My facemate is my ex's best friend. I added him just to make him feel bad.