How does a witness contact anonymous? And how do "anonymous" even verify that these witnesses are legitimate?

Just reads like a bunch of people wanting to do "something" about this and a bunch of other people trolling them (i.e. giving them false leads etc).

If I were to hazard a guess, it probably had to do with the fact that the 'suspects' in this case were all minors, and perhaps the RCMP has access to fewer avenues of investigation without any hard evidence, and the judge/magistrate would most likely not as easily grant any sort of search warrant as easily due to the suspects being minors.

I'm from Canada, and the police are generally very much cuffed at the hands when it comes to dealing with minors. Just look at the Vancouver 2011 riot. It took the RCMP over a year even with all the picture/video evidences before they could legally bring any sort of charges against a lot of the younger perpetrators.