Some families pool funds to hire a limousine to drive their teens to dinner, the prom, and the after-prom party. Don't leave the hiring to your teen. Make the arrangements yourself and specify that the driver is to make no stops other than those you've pre-authorized. Ask what measures the drivers take to prevent the limousine from becoming a place for kids to drink.
Some drivers require that kids bags be placed in the trunk, for example.
Some proms are held at hotels. It's not uncommon for teens to use private suites in the hotel for after-prom parties. In general, hotels don't rent to minors so they need a parent's involvement. A parent whose credit card is used is liable for damages which can be considerable if a party gets out of hand. Don't let your child attend a hotel party unless you know and trust the chaperones or are chaperoning yourself.