Actually, it's the fact that you're (hopefully) currently not (and hopefully not ever) worrying about someone who went missing.
I say this as someone who really doesn't like FB, and thinks that at least on a napkin it makes sense that by contributing to depression it might contribute to all sorts of negative stuff, including people going missing. That's all valid, but both secondary and kinda tasteless in this context.
Someone looking for a missing person will be happy to hear useful information about any and all avenues they could take. I'm right with you picketing companies and anyone who has a Facebook page instead of an "actual webpage", and whatnot. But people who are worried about someone who went missing? Nah. I get where you're coming from, I respect and might share it as knee-jerk reaction, but think it through. In that situation, you exhaust all options.
Would you still object if outcomes were objectively better?