As much as it is exceptionally useful to have search engines available for finding information online, they are not always the best option when you're looking for particular individuals. When your search is this refined, then you will likely want to check out a niche site that is more specialized to the kind of search you're trying to make.
This can include a social networking site, which is geared toward helping people find other people they know (or would like to meet). You can quickly and easy look up the names of your high school friends and then ask to be able to see their profiles. There, you can check out what other friends they have listed on the site. You can then find your mutual friends and ask to see their profiles as well. This way, you'll have access to whatever contact information they have posted, and you'll be able to message them through the social networking site.
Similarly professional networking sites are designed to help people connect on a business level. Many people take advantage of this form of free marketing to help them advance their careers, build client or supplier relationships, or otherwise connect in the business world.
Another form of specialized searching site that is specifically geared toward helping people find their old high school friends is alumni search sites. These are very popular online and can help you to find everyone you used to hang out with by allowing for searches using names, schools, and graduating years. These sites have been helping thousands of people find high school classmates online in a matter of a few short minutes. Of course, you will need to register with the site to be able to perform a search. Registration is free and it helps your old high school friends to be able to find you as well. Keep in mind that while searching is free, if you want to contact your friends, you will likely need to upgrade your membership to a premium level in order to access the necessary contact information. However, this nominal fee will give you access to everybody you've been meaning to contact since graduation.