It depends on what you say about the person / website, and how specific you are. If you name the accused with sufficient specificity that they are clearly identified, and you accuse them of distributing child pornography, then you might be sued for defamation. If they actually are distributing child pornography, then you have the classic defense against a defamation lawsuit (truth). If the individuals depicted are of age, you could be in legal trouble. However, if you say something along the lines of "Shocking how young these people look", especially in the context of that business, that would not be defamatory.
The link is not particularly crucial to a defamation claim, and if you simply claim that "Junior Fun Pix" (a currently non-existent company) distributes child porn, that would count as defamation. One of the elements of defamation is that the accused is specifically identified, so "some pervert" is not a specific enough claim that a defamation suit would go anywhere.
It is important to know that if you incorrectly accuse a person of distributing child porn, and make that accusation to the police, you are protected. Making a public accusation can lead to a defamation charge, making a police report absolutely will not. It's not clear exactly what you mean by "Crime stoppers" (i.e. are you referring to the organization Crime Stoppers USA?), but it is very unlikely that it is the police. Even if a defamatory statement is not splattered across the internet, communicating it to another counts as "publication". However, there is also a qualified privilege defense, whereby if you have an interest in the matter and you communicate it to a person with an interest in the matter, and do so in good faith, then even if the claim is false, you may be protected. It is an affirmative defense, so you have to prove good faith. Reporting to Redit or Facebook would probably be viewed as an officious statement, but reporting to "the authorities" even if they are not the police is likely to pass the sniff test for good faith. The circumstances surrounding the putative offense would be relevant in determining whether you have a reasonable cause for making the accusation (essentially: would any reasonable person come to the conclusion that you did?).
There is a Kafkaesque nightmare scenario where you report this to the police, and it really is child porn, but worse, the police decide to pursue you because you apparently viewed, at least for a moment, illegal footage. It then matters what country's police you report the crime to. In the US you should be safe (given US law, as noted in the other answer), but I would not say that about all countries (e.g. Iran, Saudi Arabia, which have a harsh view of all forms of porn).