Tournament
A tournament will keep teenagers occupied and give them an activity to do throughout the night. Start by choosing the game or games they will play. This can be a one of or a combination of video games, pool (if you have a pool table) and board games. Get a list of who will be coming from your teenager and if you have a white board or chalkboard, set up a bracket system such as the NCAA uses. Randomly choose which people will face each other and let them play. The winner of each match will move on to the next round. Play will continue until there is a finals match between two people. The winner of that game will be crowned the tournament champion and should win some sort of prize. Depending on the type of game and the strength of the players, the final game can become the highlight of the evening.
Match Game
This game is simple and requires only name tags. Write down the famous couples from history or pop culture (e.g. Romeo and Juliet, Mickey and Minnie Mouse, Brad Pitt and Angelina Jolie) on the name tags and shuffle them. As the guests arrive, hand out the name tags in random and instruct the players look at them, but not to put them on. When the most of the guests have arrived, have them begin mingling and asking yes or no questions to other people about who they are (they can't ask about a the other person's "name"). Eventually players will begin to find their matches. Once the player has found their match, they can then put their name tags on. If you have an odd number of people, you can add a three person combo like Larry, Moe and Curly or Huey, Duey and Luey.
Place Your Bets
Because of the concentration required for this game, it is best suited for older teenagers. Have the teens sit in a circle and deal them all out a playing card. At a signal, have all the teens attached the cards to their heads using tape (make sure the players do not look at their cards). In turn, each player is then allowed to ask one other player one question about their card (For example, a player might ask "Is my card higher that lower than Player A's?"). The player who is asked can give up to two clues about the value of the asker's card ("Your card is higher than A's but lower than B's"). Once every one has asked a question, they must then announce what they think the value of their card is. The players who get it right get a prize.