Nothing in life is certain.
That is a truth to live by, and let me explain how it applies.
I would say, without hesitation, that 96% or more of teens are simply interested in sex, or short girlfriend/boyfriend relationships, lasting only in the weeks.
when i was a teenager, i had a relationship that lasted 2 years. It was my first. i did not want a short one, or a sexually based one.
The answer to your question is that yes, most do. but that doesn't mean all of them do.
And before i leave, let me explain.
Relationships between teenagers are usually a shallow imitation of relationships as an adult. Like all things, children learn of relationships through movies, and watching adults, and they then attempt to imitate them. But, because they are just developing the tools necessary, they go for only one thing:
This is their downfall, and why their relationships inevitably fail. When one bases their relationships entirely on someone's looks, without considering their personality, there is no hope.
Hope that answers your question.