In the beginning, Islam proposes us to not make a relationship before marriage. It says in the Qur'an, surah Al-Isra' 32: Walaa taqrabu zina - Do not approach zina. This ayat is the key to a lot of relationship problems. Does creating a special relationship between a boy and a girl is in the category? I'm not trying to be harsh but - logically - I think it is. Especially because this relationship is the same kind with a 'more serious' - more dangerous relationship.
Zina is a crime - If you think the effects this can do, it's massive (It's sad a lot of people doesn't care). If it's not Allah who forbid this, no one can. Well, sexual activity is a need of everyone, and it's a double edged sword.
Now, I'm a Muslim teen myself. I know the desire of having contact with my crush -- cough sorry -- However, I still keep a 'safe distance' between us. It's a little difficult, I admit. Well, I did all that simply because once you're in a relationship, it's extremely difficult to not cross the line. You'll met more often, and you'll want to be private. Even if you can keep yourself not to cross the line, what if your partner does?
Well... I think that summarizes it. By the way, one thing you can do to hold it down is to fast... I don't do that very often but I try to do it sometimes :D
This has been a very popular topic in the internet, so i think i might share some worth-to-read links:
Relationships according to Quran - It's from this site as well
I'm sure we know what's right and what's wrong. It's in our senses. It might be possible for one to have a relationship without private contacts - although i think this is impossible. If you want to keep going, then go to marriage :)
If you have another question, please comment!