Algorithm for getting symetric vertex sets of undirected graph

Question

For my application problem, I am searching for an algorithm that can find all symmetric vertex sets of an undirected labeled graph.

My definition of symmetric vertex set is: Let $G$ be a graph with vertex set $V$ and edge set $E = \{u,v\}, u,v \in V$. If $S \subseteq V$ and there exits an isomorphism $f$ on this graph such that for every $v\in S$, we have $f(v) \in S$, then $S$ is called a symmetric vertex set.

I have searched some graph matching algorithms, but have gotten no clue so far. I am wondering if any one can give me a hint, I will work on it.