I’ve actually seen a pretty large amount of coverage of young girls of color going missing in cities where there’s a large population of people of color. Often, the cases are solved pretty quickly.
When the cases grow cold, I agree that it’s the people who are either more well-off or have some connections with local government, law enforcement etc who know how to keep a case in the news for months or years. If the child, regardless of race or ethnicity, is from a family that has limited resources or is unstable, the story won’t persist.
Also, when a kid is just walking around their neighborhood which, in the case of lower economic spectrum people, often has a lot of crime anyway, and the kid disappears, it doesn’t get the same kind of attention as when some well-off child disappears from an area that is supposed to be safe.