1st half extremely realistic, second half, not so much
SPOILERS
The first half was completely believable. I've seen in my own personal life where young women are waaaay too trusting of people they met online. It's entirely possible that Megan would have gone to meet Josh where she did and ended up getting abducted.
It kind of comes apart in some minor ways in the second half. Amy took Megan's disappearance way too well. She didn't even cry, which I think was at least partly because the actress couldn't cry on cue, hence the unconvincing rape scene later on.
Also, I can't believe the cops wouldn't put some kind of surveillance on Amy after she came forward and was threatened by the abductor even if they were still thinking it may have been a hoax and a runaway. Additionally, Amy parents didn't think to discourage her habit of taking long walks by herself after Megan's disappearance! Really?!
Lastly, the barrel thing. First, I really think Amy would have been psychologically broken by being shoved into the barrel with Megan's decomposing corpse and not capable of coherently continuing to beg for her life. Also, I'm pretty sure Amy would have suffocated in the barrel pretty quickly. Dead bodies do putrefy after a while and Megan was pretty decomposed. It would have been toxic in there but she didn't seem to even have trouble breathing.
Regardless, I think this is a pretty valid movie about internet predators that should be shown to teenagers.
S.F.W.