Induction welding is a fusion bonding process relying on the application of an alternating magnetic field to generate heat at the joining interface. Herein, magnetic hysteresis losses heating elements, called susceptors, which are made of magnetic particles dispersed in a thermoplastic polymer, are investigated. A methodology to identify the parameters influencing the heating rate of the susceptors and to select suitable magnetic particles for their fabrication is proposed. The applied magnetic field amplitude is modeled based on the induction coil geometry and the alternating electrical current introduced to it. Then, properties of the evaluated susceptor particles are obtained through measurements of their magnetic hysteresis. A case study is presented to validate the suitability of the proposed methodology. Particles of iron (Fe), nickel (Ni), and magnetite (Fe3O4) are evaluated as susceptor materials in polypropylene (PP) and polyetheretherketone (PEEK) matrices. Heating rates are predicted using the proposed method, and samples are produced and heated by induction to experimentally verify the results. Good agreement with the predictions is obtained. Ni is the most suitable susceptor material for a PP matrix, while Fe3O4 is preferable for PEEK.