In fact, I even know a few who use punctuation. Regularly.
Therefore, when I read a scene in a book that involves texting--and there are an increasing number of such scenes out there--I cringe when I see text speak used like above.
Okay, I'm not a perfect texter. I don't capitalize all the time, and I occasionally abbreviate words that are NORMAL to abbreviate (like appointment to appt.), but I certainly don't jump at the chance to turn every word into a number, and I check my spelling if I'm not sure, and I correct mistypes when I see them, and also I'm not Ebony Dark'ness Dementia Raven Way.
Therefore, when I use texting in my stories, I don't let myself overthink it. I just type how I would if autocorrect wasn't capitalizing words like "i" and the beginnings of sentences. Then I italicize it (with the possibly exception of courier, I can't wrap my mind about crazy "text" fonts in rough drafts). There. Text. Done.
(Sometimes I can't help it. I even capitalize.)
My point is, if your characters tlk n txt spk, not only does it take an extra five minutes to read, it also doesn't seem very realistic. Most YA characters have at least graduated eighth grade. Advanced stuff like grammar and capitalization has probably been covered by then.
Over 'n out.