When I send out press releases to local newspapers, I always follow up with a phone call to make sure it arrived there.
I use some of the free press sites and I also pay to have to have them posted to the larger newspapers depending upon my budget. I prefer the paid to the free because they actually get printed whereas the free sites can be cumbersome, limiting number of words and can get lost in the thousands being submitted each day. Of course, the latter is good for
SEO searches so I do both.
Not sure where you want to have your release published but I'd suggest going to the local library and pulling magazines and newspapers which are related to your topic. If the release is creative and informative, it could turn into a story. Don't hesitate to track down really local free publications that most towns have. They usually have both online and print options. I've been using a newsletter to post my client's releases lately, called AmericanTowns.com which will offer regional (and free) areas to post releases. I think it is also good idea to post releases on your own website and create a Press tab if you don't have one already. When you write your teaser for the press release postings use lots of rich keywords. I think there is a link there on how to do that.
Good luck.