If the only reason you're blogging on all those platforms is because you think it's going to "skyrocket" your site to the top of the search results, you're wasting your time.
Blog because you have something to say. Choose your platform because it's one you find easy to work with, that suits the theme and message you're trying to get across.
Blogging can potentially help your rankings, but it will take time -- and it takes an strong, well-written blog. Crappy writing that you're just cranking out to meet some artificial publication schedule designed to boost search rankings will not get the job done. And in any case, it isn't going to be quick. Blogs can take years
to attract the kind of readership and engagement that would be useful.
A blog does not help a bit simply because it exists. It helps only when it gets a significant number of social shares, links and comments.
Blogs that are written solely for the purpose of boosting rankings seldom end up fulfilling their purpose, and often end up taking time away from other, potentially more useful, marketing activities.