(n.) One who officiously tells tales; one who impertinently or maliciously communicates intelligence, scandal, etc., and makes mischief.

a tale-bearing animal betrayer blab blabber blabberer blabbermouth busybody canary delator fink gossip gossip columnist gossiper gossipmonger informer narc nark newsmonger newspaperman peacher quidnunc rat reporter rumormonger scandalmonger sieve sneak snitch snitcher spy squealer stool pigeon stoolie tabby taleteller tattler tattletale telltale tipster tittle-tattler troublemaker whistle-blower yenta