Teenagers generally use text messaging rather than e-mail for many reasons. One being that it's faster, easier, and you usually just don't see this generation e-mailing one another. Our world is more modern, along with the teenagers in it. So texting your friend instead of e-mailing them just saves time and the extra work of having to e-mail someone every time you need to talk to them. Conclusively, more teenagers use text messaging more than e-mail because it's significantly less extra.
I hope this helps :)