Facebook is a great place to find high school classmates but it should not be the only option. Explore all the avenues. One approach is to use the average search engines, be it Google or one of its contenders. The trick is to enclose the full name in quotes. Just typing "John" and "Smith" into Google's search box would give results like "John Wong" and "Peter Smith", among other Things get better if you have the middle name or middle initial. When searching with middle initial, be sure to use it with and without the period. For example, search for "Joe M Wong" as well as "Joe M. Wong". Always go for the more unique names although I did get lucky and found someone with a common first and last name thanks to his middle initial and a business photo.
There are many other social networks that you should explore. One big hassle with the web is the need to open accounts as you come across new sites. Luckily, some of the popular social networks, such as Plaxo, readily accepts accounts from the popular sites, like Google. Even if you have to create a new account with a site, take the plunge. Some sites have school networks so there may be someone you know from high school waiting to be found. I must say my own venture into Friendster, Gather, etc got me only messages from scantily clad women and no new leads.
In this day and age, the ideal contact would have an email address but you don't always get that. There are many web sites that cull info from the white pages etc to give you info on phone numbers and addresses. I used ZabaSearch, WhitePages, SwitchBoard, etc. and actually found a few people through those phone directories. Again, unique names help, although in general these phone directories also list the members of the household. If you happen to know the names of someone's siblings, high school sweetheart, or a parent, the extra info can help narrow down the results. With free weekends and weeknights, it may not be so bad, cost-wise, to call people in series until you are done with the results list, but it is better to go with the more likely names first.
With the philosophy of leaving no stones left unturned, find high school friends outside of Facebook means using search engines, coupled with using quotes to keep the first name and last name, or even middle initial, together. Join other social networks and look around. Every person found can potentially lead to another person, or more. Lastly, while email is ideal phone contacts should not be overlooked.