I'd say a pivotal tool for globalization among teenagers is the internet - with the advent of youtube and other such sites we're allowed to get a glimpse into almost every culture, something that wasn't quite as available for older generations or even with TV (TV tends to show stereotypes whereas a lot of tubers upload their own stuff).
Quite an interesting theme. Teenagers, I think, are the age group on which globalization has had the strongest impact. I speak as one who had been under it's direct influence through the internet and not only that. Think of books, films, music and media in general. Ten years ago I couldn't have found Shakespeare in English in Romanian book-shops and I wouldn't have heard of small artists or TV shows. It has influenced my life and opened up whole worlds and I believe I would have been a completely different person without globalization.
Not sure if you still need additional help with this topic, but in case you do: Globalization is a very broad topic that incorporates many dimensions, even when just seeing its impact on teenagers. One idea would be to examine the relationship between teenagers and globalization; that is, see how globalization affects teenagers, but also how teenagers contribute to globalization. Users talked about how the internet is a major contributor to globalization, which is true, but the majority of internet users today are teenagers! The exchange of information through social media outlets like Facebook and SnapChat is a perfect example of globalization, seeing as we see crossings-over of cultures, and they are being facilitated by teenagers.
Anyone can make an impact but teenages are young and are "The future" so they have the most say as the changes will be happening for them.