Has Google invented algorithmic libel?

Well, if the questions are published with reckless disregard for the truth, yes (eg., the publisher knows she’s not a prostitute).

I think a better argument is just that the auto-fill feature does not equate to publication, since the suggestions don’t actually exist until the user starts typing.

I think the best possible legal analogy (at least under US law) is liability of website operators for content posted by third parties, since the autofill suggestions are effectively amalgamations of third party content. We’ve discussed it in several threads here before, particularly as it pertains to the Chicago Reader.

In short, the Communications Decency Act (specifically, 47 U.S.C. § 230) immunizes “computer service providers” (website operators) from claims based on the exercise of the traditional role of a publisher. Google enjoys this immunity because it’s a service provider rather than a content provider.