If you didn't deactivate remote controls, pinging a 'locate device' from your Google Play Account (from Device Manager) should turn GPS on automatically. However, this requires the phone to have an active data connection and, of course, GPS line of sight. Otherwise it will give you the closest location info it has, which might be cell towers (not as accurate).
Please not that using this feature WILL display a notification on the phone stating that it has sent location information from a Device Manager request.