sympathiser

noun2

1. •
   A person who sympathizes (with a political cause, a side in a conflict, etc.); a supporter.

   • His reputation was ruined when it was revealed that he had been a Nazi sympathizer before the war.
2. •
   (no longer used) A person who has, shows or expresses sympathy (with another person or people); a person who enters into the feelings of another.

   • […] it is a sad case when the truly godly, who are cordial sympathizers, and earnest intercessours in the straits of a Nation, are stricken dumb in a day of calamity […] — 1655