We can find these constituents by comparing constituents that received the email message against the Message Open Report.
  1. Go to Email > select Email Campaigns
  2. Select the Campaigns tab
  3. Find your campaign and click Manage
  4. Select the Deliveries tab
  5. Find your email delivery and click Review
  6. Under Related Actions, click Delivery Recipient Report
  7. When that report finishes, click View
  8. Click Add results to group
  9. Click Go in the popup
  10. Fill out the required fields and click Save
Now you'll run the Message Open Report. After step 10 in those instructions, click Add results to group. At this point you should have a group of email recipients and a group containing constituents that opened the message. Now we'll create a query to compare the members.
  1. Go to Data Management > Query
  2. Click Create a new Query
  3. Fill out the required fields and click Save
  4. Click Add Group Clause
  5. Search for your group containing email recipients
  6. Select that group and click Save
  7. Click Add Group Clause
  8. Adjust the dropdown menu next to "Include contacts that are," select "not a member of any of"
  9. Search for the group containing constituents that opened the message
  10. Select that group and click Save
  11. Click Save Query and then Run Query
The results that you get will be constituents that received the message, but are not included in the Message Open Report, thus only constituents that did not open the message would be included in the query. From the query results page, you can export the constituent data in to Excel by doing a Mail Merge or you can use the query results to create a new group.