Short version: The buttons don't do this inherently as a direct result of their use. Clicking a social button doesn't "tell" Google to crawl your site.
But if the like, +1, share, (whatever else) results in a link to that page being posted someplace a search engine would see it, then yes. So, using a Twitter button to post something to my private account wouldn't cause indexing. Doing it to my public one likely would. Same for Facebook likes, and so on. The +1 button might be seen as special given it's actually owned by a search company, but here's a test from someone in June in which the poster determined that using it doesn't get you indexed, either. I can't immediately recall if there's been an official statement about it from Google, but also keep in mind that it could be seen as (self-)favoritism if they did.
Depending upon the specifics of how you're blocking access to the engines, even that still might not result in any indexing. If you have noindex rules set up, then they should be respected. If you're using something like an htaccess auth, the engine can't actually reach anything(because "login" fails) and it might not index anything at all(I'm not perfectly sure of this), but at most might keep the URL around but no content. If you've done something like set up user access rules but still present some kind of placeholder page, then the placeholder is what will be indexed. There may be other possibilities here.