First amendment applies to government. Not private companies.
"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."
The first amendment does not apply to private property, such as Facebook. That is the problem. I do not use Facebook, and am really appalled by its success and the dependency it has fostered, but it is what it is, a publicly-traded private corporation that runs a wildly successful information exchange. Since the government does not own or operate it, the First Amendment does no apply to their operations or conduct.
I worked in the regulated public utility sector while in law school and I sometimes think that the public utility model of regulation might be applied to Google's search engine to assure that thumbs are not on the scale of returned results. There you can say that 97% of online searches are conducted using Google and that monopolistic status invites abuse, and to combat abuse we impose regulation. For Facebook its a less strong argument.
Explain how the US Federal government is restricting speech and thereby causing Apple et al to be sued?