Give each person a post-it note and ask them to write on it the name of someone well known to everyone in the group. It could be a celebrity, sports person, or the local pastor. Without showing anyone, stick this to the back of the person next to you.
Everyone then mingles amongst each other, with the goal of determining their 'secret identity'. They can ask questions that can be answered with "yes" or "no" - for example "Am I a female", "Do I have blonde hair", "Am I over 50 years old", etc.
When people find their identity they can sit down until everyone has finished.