It may be true that it took some individuals calling themselves "Anonymous" two hours to discover the identities of the youth who had sex with Rehtaeh Parsons. While Canadian law prohibits the publication of identities of youth accused of crimes (on the basis that youthful indiscretions, even of a serious criminal nature, should not follow perpetrators for their entire lives), it's not all that difficult to find someone who knows someone who knows who was involved.
The police also knew exactly who was involved, and have known for over a year.
The "lack of evidence" referred to by police was not a lack of evidence of who was involved, but rather a lack of sufficient evidence that the sexual encounter was criminal. Even if they believed that Rehtaeh Parsons had been raped, the bar for laying criminal charges is "significant likelihood of conviction", and the bar for conviction is "proven beyond a reasonable doubt" -- and where the alleged victim does not make a complaint until after facing bullying for what her peers were presuming was consensual, it can easily raise doubts as to her veracity.
(The lesser issue, of producing and distributing child pornography, was the opposite: Clearly an offence had occurred, and they knew whose phone was used; but they had no way to prove which of three suspects was responsible.)
As far as I can tell, the police and prosecutors were entirely correct in their investigation and analysis of the situation. The only officials who did not do their jobs were the school administrators who failed to prevent or stop the bullying which Rehtaeh Parsons was subjected to, and the mental health workers who failed to take Rehtaeh Parsons's suicide threats seriously enough.