ちくる： more of a slang term- to tell a teacher that Jimmy smokes weed. To tell Dad that Michiko has a 30 year old boyfriend.
密告：みっこく： snitch on a crime- used in newspapers or police reports.
言いつける:いいつける： kind of a childish word - someone who says a secret without knowing they're doing anything wrong. "Daddy! The lady you called fat is at the door!"