By default, new profiles are set to private. This means that only super administrators and the member him/herself may see and access that profile's information. Private profiles do not display in search results.
Public Profiles by Default
Member profiles may be set to public by default via the administrative Members component. To do so, log in to the administrative back-end and find Members in the Components list of the main menu. Once the Members manager page has loaded, locate the Parameters button in the toolbar (top right, opposite of the Members heading). Click this. You should be presented with a series of settings. Find Default Privacy and set to Public. All new accounts will now default to public profiles.
Note: any accounts created before changing this setting will retain whatever configuration they had. For instance, private profiles will remain private unless manually changed by the user.