Pick a category such as cartoon characters, movie stars, vegetables, etc. Pin the name of one of these items on the back of each guest as they arrive. Tell them that they need to find out who they are by asking other people for help. The rules are:
1. Ask "yes" or "no" questions only.
2. Answer yes or no to questions only.
3. No removing your own name tag to find out. If you ask, anyone will help you find out your identity.
4. If you need people seated or grouped up this may be a good way to do it. Have place cards at the seat of each item. Or have a few different categories of item to guess. Then when it comes time to group up have the cartoon characters go here, vegetables there, etc.