If I have my own blog and I make posts there, it is better if I go to my social profiles (Google+, Tumblr, Facebook, Pinterest, etc.) and I copy/paste the same content of that post, or it is better if I just put there a link with a small excerpt to tease the user to click on the link to read the full story? Which strategy is better, or maybe there is a third better strategy that I didn't mention here?How can I improve my authorship rank using social media?
SEO: publish article on multiple platforms, or just link?
seo;content;social media
and I copy/paste the same content of that post, or it is better if I just put there a link with a small excerpt to tease the user to click on the link to read the full story?The latter.  So very much the latter.  You want social media entries to be short and to the point using eye-catching words and images.  Your long form content should be uniquely available on your web site with appropriate social sharing buttons prominently visible.  The more your content is shared, liked, retweeted, pinned and +1'd the better your authorship rank will be.  Make sure you have the rel=author meta tag set to your Google+ account and added to all pages of your blog.