domains for sites that looked like they were for small businesses and did a whois lookup to get their email. I contacted them each, with a unique message (you can sometimes tell what a site is about by their domain) and got some responses for web design work.
* Go to the site and ask to speak to the building site manager and ask him/her how to contact the client
* Go the companies office website and look up the business name
* Google the domain name and the business name and see if you can find any posts on social media talking about the new business. From there you may be able to track down the owner.
If there is a new business then go to the place of their business or ask around in Yellow pages. Otherwise try Whois to see if the details are listed there.
I suspect if they have the domain, they must have someone already on it, but does not hurt to have a look thanks.