I remember Diff'rent Strokes had two separate episodes on kidnapping, and I think Punky Brewster had one. Any others ?

There were 3 DS kidnapping episodes. The Bicycle Man Part 1 and 2, and Sam Gets Kidnapped.

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Andrew Carden

The Jefferson's. They kidnapped Florence thinking she was Louise.

Carol

DS had 3 I think:
The Hitchhikers (2 parter)
Bicycle Man (2 parter, not really kidnapped but still)
Sam Gets Kidnapped (2 parter)

Suddenly Susan had fake one in Susan's Ex. Oliver pretended to kidnap her and take her on a romantic getaway on a private jet.

TOW the Monkey Got Away Mr heckles kidnaps Marcel on FRIENDS and on the Nanny.. CC's dog and Nanny Fine are kidnapped on the Nanny

Mr. Belvedere was kidnapped by a lonely widow in one episode. Frank Burns was kidnapped by two North Korean soldiers on M*A*S*H. but only long enough to get them past a checkpoint.

Hogan's Heroes (http://www.sitcomsonline.com/boards/forumdisplay.php?f=71) - Eps. The General Swap and Unfair Exchange.

Soap had one and Threes Company had an episode where Jack and Janet thought Cindy was kidnapped.

There was a Petticoat Junction episode, if I can recall the story correctly, in which a Vietnam war orphan is smuggled out of the country and arrives in Hooterville. Sort of qualifies as a kidnapping, as a child is moved illegally -- although for a beneficial purpose.