Generally there will not be that many people in the noob (lvl <10) areas. It depends on your server though, if you are on a low pop server it will be possible that you won't see many people anywhere. If you want to see more join a medium or high pop server, just know the higher pop servers may have lag issues.
Also oftentimes a lot of people will be in instances away from everyone else.
You can refine the /who command. For example if you want to find out how many people are on at about your same level do a "/who 10-15" to find out how many people lvl 10-15 are on. Just know the who command is limited to 49 people, so if you get 49 you can narrow your search by reducing the level range. You can also add the location, such as "/who barrens 10-15" to find out how many people lvl 10-15 are in the Barrens area.