Names and Screen Names
Try searching on the person's first and last name first. However, this will not always bring up the person you are looking for as people don't always put their full name on their profile. For example, if you are searching for someone on MySpace, many people are using screen names and not their full name. But on LinkedIn or Facebook, people are generally using their first and last names.
If you don't get the person you are looking for, try variations of the name such as removing the last name or using a nickname. Also try location to help narrow the search results. You can also try searching without the name but with other information such as school, location, age, gender, or career to try to find the person you are looking for.