(らち) Kidnap for ransom.
(ゆうかい) Similar to 拉致、 but it has the 誘 kanji (from 誘惑- to tempt). So 誘拐 is more like a guy in a van with candy who uses guile and deception to lure the victim, and 拉致 is more like North Korean spies use guns to roust you from your bed in the dead of night and kidnap you.
(なんきん) Take someone prisoner and keep them in your basement. Not done for ransom. Used about psychos usually.