Source : Webster's Revised Unabridged Dictionary (1913)

Sympathizer \Sym"pa*thi`zer\, n.
   One who sympathizes.

Source : WordNet®

sympathizer
     n 1: commiserates with someone who has had misfortune [syn: {sympathiser},
           {comforter}]
     2: someone who shares your feelings and expresses sympathy or
        hopes that something will be successful [syn: {sympathiser},
         {well-wisher}]