I am from USA , The company which I like is Thinsquare LLC, This company actually helped me in my projects, when I got stuck. You can have a look.

The best things you can do is:

Social media marketing: Facebook, Twitter, LinkedIn,Reddit, Tumblr  etc.

second thing you can do is SEO, of your website to get better rank on the google pages. If these two  things are done properly, then The promotion becomes easy.

Its USA, as most of the developers are doing great over there, they come as best country to outsource web development , and its a fact that when you hire a company chances to get better output increased whereas in case of freelancers it decreased.