Select the "Supporters" tab of your cause account. Use the dropdown, select the "Search" option and enter the first name, last name or email address, then click on "Confirm" and click "Apply" to view the results.
Export the supporter database
If you have a Premium account you can export your search results. First enter a name for your results (and view) in the "Give a name to this view" field and click on "Save View", then click on "Export". A notification will be sent via email, with a link to start the download.