Invisible or underground sims
When I move characters from one household to another in my game, sometimes they seem to disappear underground. I can see their thoughts moving around the lot, on the ground, but can't control them or see them. Often their icon in the menu is blank too.
You should not use moveObjects to move Sims. Using it for building is ok as long as you don't over-do it. Make sure to turn it off if you no longer need it.
Use the cheat resetsim firstname lastname (name of your Sim) to get them unstuck from any situation.
I would suggest to reset everyone with resetsim * to see if you get rid of the issue.
If that does not help, try the factory resetting solution described here: http://answers.ea.com/t5/The-Sims-3/Troubleshooting-Steps/m-p/714/message-uid/714#U714
If that still does not help, it might be best to copy all your beloved Sims to the library and then move them to a fresh town.