Actually, Karma stands for action. Karma is the action that's committed; good, bad and neutral. The vast amount karma is neutral. Once an action is completed (like theft), it leaves a mental imprint that will "bloom" into an event later that will be similar; like the others said, theft will result money problems or loss of property or something like that. It's not eye for an eye though, the results are muddy at best because it's mixed with other karma.

Most important to remember is that karma RARELY affects us during the current lifetime. This means that the people that steal from you won't feel the effects until the next lifetime or a hundred lifetimes from now or much longer. This is why people can never understand what they've done to receive horrible occurrences like disasters or car wrecks; it's from karma committed in past lives.

And incidentally, wishing bad karma on someone has no effect on them. It's only bad karma that you yourself are creating.