can't search by first name last name; WordPress dashboard
First check that you have Automatic Wildcards enabled, navigate to Administer -> Customize Data and Screens -> Search Preferences, is the first option.


  If enabled, wildcards are automatically added to the beginning AND end
  of the search term when users search for contacts by Name. EXAMPLE:
  Searching for 'ada' will return any contact whose name includes those
  letters - e.g. 'Adams, Janet', 'Nadal, Jorge', etc. If disabled, a
  wildcard is added to the end of the search term only. EXAMPLE:
  Searching for 'ada' will return any contact whose last name begins
  with those letters - e.g. 'Adams, Janet' but NOT 'Nadal, Jorge'.
  Disabling this feature will speed up search significantly for larger
  databases, but users must manually enter wildcards ('%' or '_') to the
  beginning of the search term if they want to find all records which
  contain those letters. EXAMPLE: '%ada' will return 'Nadal, Jorge'.


Check your display and sort name, navigate to Administer->Customize Data and Screens->Display Preferences at the bottom you have two fields, which by default should look something like this: 

Individual Display name format: {contact.last_name}{, }{contact.first_name}

Individual sort name format: {contact.last_name}{, }{contact.first_name}

If you want to search always by first name you can change the sort name format to {contact.first_name}{ }{contact.last_name}, now this will only apply for new contacts and not for the existing ones, you will have to update the sort_name for the existing contacts, there was a discussion in the forum about this.

If you search for "Adams," in the demo site you'll see that the result will be "Adams, Lou", as far as I'm concerned, this is expected behaviour.

Edit

Forgot to mention that you can use wildcards like: %joe%, that should include Joe Johnston and Johnston Joe if there is a existing contact by that name.