More realistic than your teen being hunted down by some random predator is your teen being teased, hazed, or even physically bullied by a person or persons with a specific grudge against him or her. Inasmuch as social media and location-based services make it easier for us to learn more about our friends, it also gives bullies more ammunition to use against their targets, just part of the much bigger trend of bullying (particularly emotional bullying) intensifying in the digital age.
Related to bullies (but more specifically relevant to kids in their late teens) are stalkers – romantically obsessed former flames (or would-be flames) who latch to the objects of their obsessions and refuse to let go. For these folks, check ins can serve as a how-to guide to create chance encounters, keep up with potential romantic "rivals," and generally make their targets' lives miserable.
-- Mind-Numbing Conformity
Certain places don't make for rock-star level check ins: Grandma's assisted living facility, the coin and stamp store, the hobby shop, and so forth. And others may be almost required to show that you're with it: particular parties for example.
Teenage life (like life in general, come to think of it) is a precarious balancing act between being who you want to be and who you think everyone else thinks you should be, and check-in services just add one more layer of information and monitoring to the sometimes nasty little fishbowl that is middle school and high school life.
For the places that leave you less cool just for having associated with them, the obvious answer to this is simply not to check in. And as for running with the pack to the places that be ... well, it's something teens will have to grapple with regardless of their access to location-based services.
-- Create a Living Diary