Although due to the amount spam which is being sent each day, many people wish not to publish their e-mail address. However, if you ask them to give you this address, the person shouldn't have any second thoughts and would probably provide you with his e-mail. A lot of people forget login credentials to their e-mails accounts and change the address, but usually when you ask somebody for an e-mail address, he will give you his primary one. When you have the e-mail, it's sometimes possible to figure out the person's name, since a lot of people use it as a user name. However, in most cases the user name will be something like "flower34" or "joker1000" and hence you have to use some other method to obtain the person's name.
You can obviously use Google or any other search engine which can give you some decent results if the person published his name and e-mail on some website which has been indexed by Google. In this situation, you will get your information without paying anything. However, if you want to get some more detailed information about the e-mail's owner, you can use a reverse email lookup. It's quite a new service which will work with most of the US e-mail addresses. To learn how it works you can visit an email lookup website and simply enter the address in a special box. Once you hit search button, you will have to wait for a while(usually just a few seconds) to get the results delivered. At first you will be presented with just a small bit of the data obtained from database, but if you decide to pay, you will receive the full report.