I've taken a particularly keen interest in this as the girl and her family live round the corner from where I used to.. im surprised that its taken as long as it has to gain mainstream attention.
I'm holding out hope that there's a perfectly rationable explanation for her disappearance, I hate jumping to conclusions that its family although I know this is the case most times.
I would have thought most of the facts would be fairly easy to verify - if she stayed with a friend the previous night, what time she left there, who was where on the thursday morning etc. Step mom is supposedly the last one to see her but she texted boyfriend AFTER step mom left for appointment. That implies to me that if something untoward has happened to her then it had to have been between the last time she text boyfriend and the time she was reported missing.. not earlier in the day as I have seen be suggested elsewhere.
Also most phones, laptops and tablets can be tracked locationally nowadays...
Another thought - my phone, laptop and tablet are linked to the same google account so any bookmark, page visited open pages etc appear on ALL devices linked to the account.. just throwing it out there