Good icebreakers for large groups include partnering people together and asking them to interview each other for five minutes to learn something new. Large groups can also form a circle and randomly ask another person in the circle to share something about himself.
Facilitators can divide large groups into groups of 10 people to complete a scavenger hunt in the local area. Another good icebreaker compiles a list of interesting accomplishments or traits such as "first-born" or "graduated from college" and asks the group to mingle to find people who meet the criteria on the list.
Large groups can also break the ice by singing a song together, dancing to songs while switching partners every few minutes, and playing a game of telephone in a few separate groups to see which group deciphered the message correctly.
Facilitators can organize an introduction game in which parties pass out candy to people they have met in the crowd or to collect certificates, buttons or swag from each person they introduced themselves to during the event. The purpose of icebreaker games and activities is to encourage people in large groups to network with each other, learn something new about others in the group and collaborate.