sympathise vs sympathiser

sympathise is not a noun while sympathiser is a noun.

Word	Noun	Adjective	Verb	Adverb
sympathise	No	No	Yes	No
sympathiser	Yes	No	No	No

sympathise (noun)	sympathiser (noun)
	someone who shares your feelings or opinions and hopes that you will be successful
	a person who commiserates with someone who has had misfortune

sympathise (verb)	sympathiser (verb)
be understanding of
to feel or express sympathy or compassion
share the feelings of; understand the sentiments of