I don't know of any credible story about people being prosecuted for Google searches. The prosecutions for Facebook comments tend to boil down to the police arguing that the comments are threats, which fall into one of the exceptions for unprotected speech.
So, for example, if I was kicked out of a restaurant for not wearing shoes I couldn't generally claim free speech protections for my lack of footwear. However if I did so as part of some theoretical organized protest involving shoes then I could, as in the second case my unshod state was clearly intended to convey some message.
As to "substantive speech," the bar is low. Substantive in this case means just that it communicates a meaning. The meaning doesn't have to be important. Physical expression, like wearing shoes, involves a higher bar.