"last" command not working properly

Solution 1:

Always use man X directly on the Mac itself to see what is available for command X. The reason is that OS X was originally based on BSD and not GNU (most likely to avoid the GPL) so you should not follow Linux tutorials for MacOS.

Solution 2:

The 'last' command on a Mac has no -s option. Not all Unix commands are implemented the same on a Mac. Mac tends tends to use original BSD commands. As to why 's' isn't an option on the Mac, according to @Mark, it may be due to the difference in BSD (Mac) and GNU (Linux). There are most likely differences between the two.