Below is an expanded version of my response (I sometimes write comments that are longer then the blog post they are addressed to, but I try not to 🙂 ).
I think this is two separate (though related) questions.
One is the presence vs. absence of parents (or parental figures) In most cases, this is a question of realism, since (like it or not) parents are a major factor in the lives of most young adults. The only teenagers I've known, for example, who operated largely without parental supervision (or even presence) were rich.
But the question of "involved adults in some positive capacity?" is a different issue. As Bill points out, many parents are lousy. In some cases not without reason, but parents in books should run the full range they run in real life, from spectacular to horrible. That's life.
My characters, in very general terms, often have families that they chose, usually to replace the ones they grew up with (so, "family" in the queer sense, as it's put in the introduction to the William Burroughs book Word Virus). Some have good parents, though, or sometimes a good one and a bad one.
Of my two most important teenage characters these days, one (Ron) grew up with horrible parents (several of them). The other had parents who were pretty good, as long as she was doing what they wanted her to do. Both had to run away and find other parents (or some equivalent), and neither is going back. (They know each other, at least a little, but they have not yet figured out the similarities in their lives. I've planted that for later. 🙂 )
But, on the other hand, Jan Sleet had a really good upbringing (with one parent – the sane one). Marshall apparently did also. As did starling, who, as I said last time, had a very normal early life, as far as we know.
But they all did have parents, of some sort.
But there are those who don't of course, and there is also the very powerful wish fulfillment of those (Harry Potter, Clark Kent) who find out that the poor hapless earthbound folk who raised them are not their real parents, that their real parents were special and they are special. Doesn't happen much in real life, but it happens a lot in stories because it's a myth that people want to believe.
Looking back, I have devoted a lot more attention to the cases where the original parents were bad, and I've barely touched on those where the original parents were good. That made me think about a line I'd heard once about good families and bad families, which turned out to be from Anna Karenina by Leo Tolstoy:
Happy families are all alike; every unhappy family is unhappy in its own way.
It turns out there's even a statistical principle based on this, called the "Anna Karenina principle" I guess I've been following that, though I admit this was not a conscious plan.
Oh, and Emerald Barnes posted a great Peanuts comic strip. I will admit that Snoopy was one of my earliest role models as a writer. I'm really tempted to start my next story with "It was a dark and stormy night." And, based on my very initial thinking, it will show more of Jan Sleet's relationships with her parents. Both of them.