Constituent accounts created by the Tell-a-Friend feature will have an Origin Application Type of Tell-a-friend.
Locating these constituents can be done by creating a query. To find when they were created, an "and" field clause must be added to your query using the Creation Time field.

Additional fields may need to be used to target the spam accounts. You can use query results to create a group and contact support to remove the records in mass.

To query by Origin Application Type:
  1. On the Query Builder tab > Select System from the Field Type drop down menu.
  2. Select Origin Application Type from the Field drop down menu.
  3. Click Add Field Clause.
  4. In the pop up window, Select Equals from the first drop down menu.
  5. Select Tell-a-Friend from the second drop down menu.
  6. Click Save