So far, no LGBT character has 'organically' come up in the story.
Speaking as someone who is Bi and in a homosexual relationship, The above quote from you is all I care about. If, in the creative process, you come up with a cool character who fits your story and is fun to read... and happens to be gay... then by all means write about the character.
If you're trying to get me to read by shoehorning a character who you think I'll identify with because of who he/she boinks... I'm sorry... but I'm not going to care.
But here's the test for you. Find a show or book with an LGBT character that you like watching or reading about. Now, go through all the motions of that story, and pretend that this character is straight. If you do that and you still like a character, congratulations, you've found a good LGBT character (yes, some elements don't translate well... like coming out... but unless you want your YA novel to be a coming out story, it shouldn't be a big deal coming out. Just drop it in a side comment and move along with your story. Don't throw a big party about it.). And that test works for a whole host of characters you can't identify with because of differences in sex, sexuality, skin color, or religion. I mean one of my favorite characters I've created is a 16 year old girl. I gotta tell you, as a 32 year old man, never once have I been a 16 year old girl. And when I started developing the character, she was a he (No, she's not Trans... I made the character for an MMO and wanted to recycle some of my characters for my own story. When I came to this one, I felt the origins didn't work and I needed to retool. Somewhere in the retool, I flipped the gender and got a better story for my effort.).
And here's the thing, I don't know how your character development process works, but I tend to "meet" them rather than create them, and let them tell me about themselves. Sometimes the character will tell me "I'm gay" right out of the gate. Other times, they're very subtle about it. Perhaps you already wrote a gay character... they just haven't come out to you. Yet. They're waiting for you to get to know them more.