Indirect Ice-Breakers
Because you are 'entertaining' strangers you are constantly 'breaking the ice'. Ideally it should start at the beginning of the event and never stop.
As people approach the venue they should be 'greeted' by signs / people that make them feel welcomed.
Then greeted again, as they enter the actual event space.
Then continually engaged throughout the event by hosts, display tables, 1 minute videos ...
The more 'engagement' options you have the greater the chance they will return.
Direct Ice-Breakers
Everyone wants to have fun at an event. People are scared to Mix n Mingle. It's your job to create the conditions that make it EASY to Mix n Mingle.
Balloon Hats
I once hired a clown to make crazy Balloon Hats for a group of strangers at an event. It's hard to feel intimidated when everyone has a colorful wobbly hat.
The event was an absolute success because of the hats.
Christmas Party for 20 Small Local Businesses
A large room in a resort, 20 large tables.
The event starts with the Host (me) announcing, "I have 2 bottles of expensive champagne here for the Business that makes the most noise when I read out your name."
After all the names were read, the ICE was well and truly broken AND each table new which Business was next to them. The energy went from ZERO to HERO. The night was a brilliant success.
Which Side of Town
Divide the room into groups (where people are from - the north, south, east and west) and play a game with interaction.