In this work, we present a facile synthesis of FeCoNiPt alloy nanoparticles (NPs) with tunable platinum content (10–30 at.%). The NPs were produced by medium-assisted solid-state reaction using acetylacetonate metal precursors. The structural characterization (TEM, HRTEM, STEM-EDS, and XRD) reveals that the obtained FeCoNiPt NPs exhibit a uniform morphology with an average diameter of 3–7 nm and crystallize in a single-phase face-centered cubic solid solution. Increasing the Pt content leads to lattice expansion and a systematic increase in crystallite size, consistent with the larger atomic radius of Pt. STEM-EDS elemental maps confirm homogeneous incorporation of Fe, Co, Ni, and Pt across individual nanoparticles, demonstrating the successful formation of a multicomponent alloy. This study demonstrates that tuning Pt content in FeCoNiPt multicomponent alloys enables precise modulation of d-band electronic structure. The proposed synthesis approach is simple, cost-effective, and scalable, offering a promising pathway for designing Pt-optimized electrocatalysts.