If you ever visit Shanghai in Summer time goto the major malls. There are thousands of teenagers. They many hang out at nighttime simply because the days are too hot for them to be in the sun.
References :

1. Boys & Girls like to hug until they orgasm in random places like on an island in a freeway or a park bench. They just hug for hours until it happens (at least that's all one can assume is happening).

2. Internet cafes. Millions of kids playing World of Warcraft until they eventually die of heart attacks and smoke inhalation (you can smoke in them).

3. Most of them hang out at school! In China summer holiday is another way to say "more school". During the school year most kids go to school from about 7am to 10pm. In the summer though, it's party time, only about 6hrs a day!

4. On mom's sofa watching tv or sleeping. Due to lack of control over their lives Chinese kids find that staring blankly at tv screens or never getting out of bed is a hoot. When asking a cross-section of 100 kids "What's your favorite thing to do in your spare time?" Sleep and tv always score in the top 2.

5. KTV. If you're a rich kid with a few bucks, the ultimate way to pass the time is karaoke and prostitutes! Karaoke bars in China are often private rooms where you and your friends can sing your favorite love songs to each other (Titanic soundtrack is still #1) and choose from trains of women that come into the room to be chosen for sex. Only 17? That's ok, just pay more money.

6. Here's a universal activity for teenagers; aimlessly wandering malls. Perhaps you and your Chinese friends can both find this activity amusing.

Hope that helps answer your question.
References :