Ask your friend to write you his e-mail. Better if it will send to your email a virtual postcard or a song. So you learn Inbox of the desired recipient.
Go to one of the social networks that you visit most often. Perhaps familiar with the right address you have in your friends. For example, to find email address in "My world", click on the @ sign of the user. Further, the proposed window click on "Copy link address". You need to open the "mail" tab and then click "Write letter".
Locate the "to" field and paste the copied line. The displayed entry is the desired one. e-mail address. You can now chat with their friends via email. Using this, you can see the email and other people in this social network. If this method does not suit you, then use the other search options.
Type in a search query the name of the person. The more information you know about the person, the better. Maybe the system will give the data on it if it is somewhere registered in a network, for example, has its own page on the forum or blog. Maybe this version will not give you the results. Then proceed differently.
Use paid services on the Internet that help to find people, but rather, information about them. But this method is good if all the search options email address is already used. Maybe you know people who are in close or family relationships with the target person. You can ask about the address of the mailbox from them. But plan your conversation, not to be Intrusive. That is, consider all the possible questions of the interviewee and your answers to them.
With a strong desire to find the email of the desired person is quite possible, however, the use of all the options takes some time. But if you try, the reward for the work done will be a treasured e-mail address.