A modular reuse-based design methodology has been one of the most important factors in improving hardware design productivity. Traditionally, reuse involves manually searching through repositories for existing components. This search can be tedious and often unfruitful. In order to enhance design reuse, an automated discovery technique is proposed: a reference circuit is compared with an archive of existing designs such that similar circuits are suggested throughout the design phase. To achieve this goal, methods for assessing the similarity of two designs are necessary. Different techniques for comparing the similarity of circuits are explored utilizing concepts from different domains. A new similarity measure was developed using birthmarks that allows for fast and efficient comparison of large and complex designs. Applications where circuit similarity matching can be utilized are examined such as IP theft detection and reverse engineering. Productivity experiments show that automatically suggesting reusable designs to the user could potentially increase productivity by more than 34% on average.