A location of a fracture can be determined in a wellbore. Micro-electro-mechanical (“MEM”) devices of different sizes and shapes can be included in a sweep and injected into a wellbore. A MEM reader can be positioned within a downhole tool for detecting MEM devices in the wellbore after a sweep returns to the surface of the wellbore. The MEM reader can be disposed in the wellbore for measuring the position of the MEM devices remaining in the wellbore. A location, size, and shape of a fracture in the wellbore can be determined based on the position of the MEM devices in the wellbore.