The idea of "social media" fame is perplexing, but I'm an oldie.
That said, it's one of the new means of celebrity and it's not all that fundamentally different than some of the old means of celebrity. Earlier generations (and current generations) worship movie stars, music stars, sports stars, political stars, etc. And only a fraction of those "stars" has more talent at their chosen profession than the average amateur doing the same thing (sports is hardest to fake talent... the others it's pretty easy).
It's not unhealthy for teen girls to idolize teen boys (and vice versa). It's a baby step towards real romantic relationships that follow sometime thereafter. Most of the time, it's harmless. And it can be a healthy way to channel raging hormones.
Obviously paying to have your child engage with the object of her affection is a different subject. I don't see what is ultimately wrong with doing something special for your son or daughter on their birthday or every once in awhile--spending within your personal budget. That could mean buying concert tickets and/or meet and greet passes for her favorite band or singer; getting her great tickets for her favorite sporting event; or taking her to a comicon to meet her favorite geeky heroes (and paying $25 for that autograph). That's not all that different than a parent buying a child an opportunity to meet her favorite social media star. We may not understand the appeal of these guys, but this is an experience, not a thing. I am much more apt to spend money on an experience than a thing, because it tends to bring more pleasure in the long run. When these girls are 30 years old, looking back on the day their parents got them backstage passes to meet some guy from Vine, they will look back with fondness, bemusement or embarrassment. But they will probably think of it and smile, in any event.