1. Consult the Princeton Dept. of Art & Archaeology's Department Style Sheet .
2. See the CAA Publications Style Guide (College Art Association).
3. Style Manual for Art History (Chicago Manual examples), from Lee Sorensen, Visual Studies Librarian at Duke University.
The Chicago Manual of Style does a good job of providing examples of citing different kinds of social media platforms.
The online version of MLA provides guidance in a few different sections: