First! See this link one link and judge for yourself:
then, write something around this link. One possible example:
Dear [company]. I recently became aware that you advertise on Reddit. This is very concerning to me because Reddit is a website at least partially built around the exploitation of children in my opinion.
please read the detailed incident below. In it a minor details experiences of being forced to look at pornography and being stalked and harassed on Reddit.
If you further investigate you'll find that the Reddit as a system is built in a way that does nothing to prevent such cases from happening. Age is not verified at the time of signing up for an account and underage accounts have no special protections, and are not protected from being privately contacted.
I'm not sure if you are aware of media reports speculating that pedophile Jeffrey Epstein's main accomplice, the recently arrested Ghislaine Maxwell operated one of Reddit's most powerful accounts https://www.dailymail.co.uk/news/article-8506313/Ghislaine-Maxwell-secretly-operated-one-powerful-Reddit-accounts-time.html
While I can't personally verify the truthfulness of such media reports regarding the exact name of the account Ghislaine Maxwell used, the fact remains that pedophiles are currently being able to freely contact and exploit children on this despicable website with the full support of its administration.
The website's leadership has long turned a blind eye to this issue. In fact a former Reddit CEO Ellen Pao recently announced that she knew about Ghislaine Maxwell's actions, specifically "her supplying underage girls for sex" https://nypost.com/2020/07/08/ex-reddit-ceo-ellen-pao-knew-ghislaine-maxwell-allegations/ . These are fomer Reddit CEO's own words.
So while this website tightly controls content appearing on its pages with strict moderation of deleting content including for seemingly trivial reasons (compared to the discussed above) they refuse to act to protect children and to take a stance against pedophilia. Please don't take anything I say at face value and investigate for your own benefit.
The above is just one example everyone please feel free to write your own.