Some websites where you can reconnect with old friends for free are Alumni.NET and Classmates.com. Both of these sites allow you to search for and post messages to old friends. However, while Alumni.NET is free of charge, only the basic membership on Classmates is free.
If you want to send an email or personal message to a friend on Classmates, a paid membership is required, however, you can still use the search features on the site with a basic membership.
Another place to reconnect with old friends is Facebook. Facebook is a social networking site that allows you to connect with and send messages to friends for free. You can search for friends by name, school attended, region and many other parameters. The Facebook Messenger application can also be downloaded for free on a mobile device so you can chat with your friends anytime.