FAANGs all have child safety departments where you can get paid and do good.
But even at an algorithmic level, it seems like there are all kinds of red flags you could pull out of public posts and do a much better job of redirecting potentially victimized people to some organisations doing meaningful work to help victims.
How many categories does my online profile fit in based on all my interests, and how many hundreds of bright people are wasting their lives to discern that I happen to like A + B + C and I'm in financial bracket F, with political leaning G ... to try to show me an advert I'm probably just blocking anyway.