Do a facebook page and join every students page that you can.
I dont know much about that type of advertising but I imagine that if you friend request thousands of students from different schools the word would spread rather quickly. They also can sell you targeted adverting for fairly cheap from what I have heard. Pay per click style.
Once your site is properly promoted and getting the traffic that it should then approach companies whom also target college kids to advertise on your site. I would hire a advertising consultant or sales person at that point to do the selling for you.
Take this into consideration. New York City has a delivery service dedicated to delivery alcohol to households. Many times when you order the alcohol they ask you for identification information and they scan your information to make sure a legitimate ID is being used and then they review it again upon delivery. Issues? If something goes wrong, such as a death from alcohol abuse, some can scream CAMPUSBOOZE and not only shut you down but put you into jail