How do you kidnap a Sim in The Sims 2?

That isn't possible. But you can have sims taken away by the Social Worker if they are neglected or teen sims will runaway if they have a -20 daily AND lifetime relationship score with every other member of the household.

ACTUALLY, it is possible. you have to hack into the game using what we call mods and hacks. there are special mods for each thing.- different person from one above :3