Get PR by commenting

Hello,

Can i improve my website rank by publish it's url in a comment in blogs, forums or even in facebook?. Is it considered as +Backlink?

Yes it's considered backlink but don't overdo it. Stay away from spammy forums and auto approve comments on pages with 100's of obls, focus more on quality. Keep in mind these types of links are more useful for diversity than for improving your rankings

As long as Google can index it, it will help you to improve your ranking.
Make sure you have a diversified backlink profile (so build links of different types, not just blog comments), post high quality comments/posts to avoid penalization and focus on non-spammed websites + best would be they allow d0f0llow links.