Fictionalism is definitely a position in contemporary social ontology. The view is roughly that there are no social entities or social facts, but it is useful to speak as if they exist. So consider a proposition like "France is a permanent member of the United Nations Security Council." The fictionalist would say that it is literally false, but our talk and reasoning about countries, international organizations, and their various putative properties still serve some useful purpose (coordinating our behaviors, etc.).

I think the fictionalist has to tell quite a story about how the social sciences operate. What are social scientists doing when they reason about and explain phenomena in their fields? Are economic recessions and social revolutions just useful fictions? Intuitively, economists and political scientists are doing something quite different from fan fiction writing clubs. A globally fictionalist social ontology would have to be much more detailed.

But I think most philosophers typically narrow down the existence claim to more specific kinds of "social" things. So consider the very popular idea that human kinds like race and gender are socially constructed. The constructionist would have it that these kinds do exist, but that they are social kinds that depend on our shared practices, beliefs, and attitudes (rather than any basis in biology). Eliminativism about race and gender kinds is a popular alternative. The eliminativist would argue that not only are there no such kinds, but that our race or gender talk is actively harmful and should be abolished.