They were hiding amongst us.

They had a immigrant rights leader on CNN saying many immigrants' attorneys are reporting that their clients "have been disappeared." They don't know if their clients were put on those flights. The Trump administration claims they don't have to tell anyone who those people are that they sent to El Salvador. They could be minors, your neighbors, people here legally, even US citizens. CBP's recent sweeps netted exactly those people.

We. Don't. Know. Who. They. Are.

Marco Rubio can roast in hell for the rest of eternity.

if some are US citizens, asylum seekers, innocent bystanders etc., would not their friends/relatives be making it known by now that they are missing? Are their any news reports of such?

Of course, most of us would first turn to local law enforcement (police, sheriffs, etc.) and probably health organizations.

When you get no satisfactory response do you send an inquiry to your state police, FBI (now subverted), DHS (now taken over), private security firms (Blackwater as an example), foreign governments that are known to take payments for "black sites", etc.?

I don't know if you remember or knew about the Pinochet "disappeared". That was caused by the Milton Friedman Chicago School of Shock Capitalism. Exactly what is happening here.
https://en.wikipedia.org/wiki/Human_rights_abuses_in_Chile_under_Augusto_Pinochet
https://en.wikipedia.org/wiki/The_Shock_Doctrine

Sorry, probably too long an answer to your simple question.

rather than law enforcement (although if a relative or friend went missing I would certainly talk to law enforcement as well).

So then, I find it a bit curious we have apparently not heard of such searches or investigations, at least not yet. Maybe it's because most or all of those deported were members of the target gang - I dunno.

And I apologize if the tone of my earlier response to you seemed a bit strong. I looked for a good emoji to convey that but I'm not an emoji type of person.

Of course, joy in the humiliation sends shivers up their spines.
https://en.wikipedia.org/wiki/Schadenfreude

against humanity, is not too far away. The felon is obsessed with causing cruelty to the highest degree on those who do not give him loyalty. hmmm..... tyrants are not judged well in history.

I forget who said it.