Spreading URL on social networks improves pagerank?

It's considered spam if you're posting the URL on third-party posts without adding anything related to the post. Anyway, I believe this does not go a long way towards pagerank because more are taken into account the links you have in pages on the same subject and not at random. In addition, social network traffic is usually more targeted and what is worth more is organic traffic. Of course, it is important that your site have a presence on social networks.