CKEditor configured MediaEmbed button doesn't appear in toolbar
I managed to resolve my problem but didn't have time to post it in here. It was simply misconfiguration...

First you need to install Widget, Lineutils and oEmbed plugins in CKEditor's plugin folder.
Then you need to specify the path to the plugins folder in CKEditor's module configuration.
Finally, in each of CKEditor's profile, you need to enable the plugins and move the oEmbed icon to the profile's toolbar.
Clear Drupal and browser cache and it should be working.

That's it!