People see me as the cute innocent girl, but I don't think I could be any more interested in sex.
I'm constantly reading smutty romance novels and I love learning about sex.
There are also plenty of introverted people who date, have active social lives, have sexual partners, or some or all of the above.
Finding potential romantic or sexual partners is, in my opinion, very much like finding friends.
In observing, you might notice other people, or a person, who catch your interest.
I realize this may not be a comfort, but in spite of how it might seem, there are plenty of 19-year-old folks (plenty of folks of any age, for that matter) who haven't had dating or sexual experiences, or haven't had dating or sexual experiences they've enjoyed.
If you enjoy reading, for example, you might enjoy joining a book club or attending poetry readings, where the groups can often be small, and you can interact (or not! In larger group social situations, you can focus on getting to know the people nearest to you, rather than feeling overwhelmed by the whole entire crowd and going into complete introvert mode.
If the people nearest you aren't people you feel compatible with, you're allowed to just be quiet and observe.
The ability to develop friendships or other types of relationships really does depend on the people involved to put the energy into interacting and getting to know each other.
Put another way, one can meet all sorts of folks at a party, but if it's noisy and crowded or the party is centered around something specific (such as watching a football game) it's unlikely they're going to be able to get to know each other well, let alone develop an attraction for each other.