1.Texting their friends
Basically the basic activity every teenagers, both in Thailand and the other parts of the world, does nowadays. The time they choose to do this is usually in the evening, but Thai teenagers , mostly students, take it to the extreme and also do it during their classes as well. It can be useful for them to socialize, but only in the right hands. For some countries , particularly Thailand, it may seem to have more disadvantages than advantages.
2.Watching TV
Since the coming of mobile phones, TVs' popularity among teenagers has greatly decreased. Fortunately, there're many fascinating and "educative" television dramas in Thailand, which can successfully grab the teenagers' attention. Alas, they still have some drawbacks, as most of them represent the same type of people over and over again. Even worse, Thai teens seem to accept and memorize those behaviors of the bad guys ( who constantly fight for "love"). There may be some of them who still have some senses about right and wrong, but that's a few.
3.Keeping up with Fashion
As what i have said above, Thai dramas are very popular and is the topic Thai teenagers will most likely talk about first. So, celebrities in Thailand are like the fashion leaders. Thanks to mobile phones, internet and social medias (mostly Instagram), It now has become a trend to report your every moves to your friends and strangers over the internet. That, can't be done without proper clothes and fashion.