I understand SharePoint 2013, unlike the previous versions, have been removed lots of statistic reports. My only requirement is to track everyday which users have login to SharePoint or not. Is there any way to track without access the back end (e.g. check IIS raw log)?
I do not know of anyway to look only at if a user logged in or not. What you can do is go to the site settings, site collection administration, and then audit log reports. I would run a custom report or a content viewing report depending on the version of SP (online or hosted). Online SP does not support content viewing auditing but you could get a decent feel for how active your users are by including Opening or Downloading and Searching Site Content.
Hope that helps!