Nouns

(n)fink, snitch, snitcher, stoolpigeon, stool pigeon, stoolie, sneak, sneaker, canarysomeone acting as an informer or decoy for the police

Verbs

(v)hook, snitch, thieve, cop, knock off, glomtake by theft“Someone snitched my wallet!”
(v)denounce, tell on, betray, give away, rat, grass, shit, shop, snitch, staggive away information about somebody“He told on his classmate who had cheated on the exam”