The first option
Try to read mails from your ICQ client. For this you need to become a system user ICQ. Go to the website and complete the registration process, that is, on the next page, click the right mouse button on the active box to "Register with ICQ" (it is located on the top panel), complete all fields and click on the big yellow button "Register", complete the procedure by clicking the link that will be sent to your email. Then on the top panel, select the active field the "Download" and download the latest version of ICQ for your computer, install it. Then restart the PC and log into the program. Now you can start to search.
In the search box search for ICQ number, then press "search" (shown in the magnifying glass). After a few seconds you will see the profile of the user whose number you entered, if it's pointed your e-mail address, you will see him. Keep in mind that the ICQ number must be entered with spaces or dashes after every 3 digits, that is not 123456789, for example, 123 456 789 or 123-456-789, otherwise the program will not be able to recognize it and give you information.
The second method

It is suitable for those who do not want to become a user of ICQ. Go to the website and the sign "Find a friend" (green on the left side of the screen) in the "ICQ Number" enter the number you are interested in finalize, then press the "Search" (located at the bottom of this field). If the ICQ user has indicated in their profile an email address, you will see him. Remember that there is room on the contrary must be entered without any spaces or dashes, just the 9 digits in a row, otherwise it simply will not be identified.