The boron nitride polymorphs were explored using the anharmonic downward distortion following (ADDF) method with the energy value of the density functional-based tight binding approximation modified by the inverse of the volume of a unit cell. Twelve novel boron nitride polymorphs were discovered. Previously, it has been difficult to search reaction pathways connecting two-dimensional structures such as hexagonal boron nitride to three-dimensional structures using the ADDF method. This problem was partially resolved using this approach.