To prevent your stuff from getting stolen:

• Monitor who enters the party. Don't let people in that no one knows. A guest list makes this easier. Having an "everyone is welcome" party is the quickest way to get your stuff stolen.
• Hide or protect valuables and lock areas that you don’t want people to enter.
• Keep the party in a central location of the house.
• Avoid letting people get intoxicated.
• Keep an inventory of your stuff and check it after the party.
• Call the police and report any missing items.
• Pay attention to people who leave early, or people who come with backpacks.