When looking for a website's creator, scroll to the bottom of the site's main page, where most websites have a "contact us" or "about" page with information about the site and its owner. If there is no information about the creator on the site itself, run a domain registration search using a site such as Whois.com.
Almost all professional sites have an information page showing the owner of the site and sometimes its creator. If the site is very large, it is likely that the it was made by a team of people, and the page may instead display the name of the company or group in charge of designing it.
Sites without this information must still keep the owner's information and site registration history on file. Domain registration searches can sometimes show you this information. Using a site such as Whois.com, type in the URL of the main page and run a search. A domain search reveals the name of the registrar, the referrer, and the update, creation, and expiration dates of the domain name.
Owners can prevent their name from appearing on searches if they wish to remain private. In this case your last option is to attempt to contact the owner directly through the site. If there is no contact page, this may prove difficult, and if the owner wishes to remain completely anonymous, he may ignore any contact attempts.