It depends what you mean by "work". Do they work to get the news out there about your new business/website? Yes. Do they work to bring in sales and traffic? They can do yes. Do they work to increase rank to your site? Well they can do yes as they are usually high authority sites although many will no-follow your link.
But you can't just write one press release and submit it yourself or even pay someone to do it for you and pay a press release / writing / submission service to do it for you and then expect that to be the do all, end all to it. You might get a bit of a boost by way of traffic, and some big names in the industry might come to learn and know about your site. But eventually, your press releases will get buried under new ones and soon be forgotten about. Although your press release itself should remain. What works better is if you do it regularly like once a month or something but only if you have something press release worthy to write about. However, you can take any event small and large and make a press release about it.
Just hired a new team member? Press release it!
Just expanded your work space with a new office? Press release it!
Just started selling a new product or brand line? Press release it!
Just signed up to the better business bureau? Press release it!
You get the idea!