Density functional theory calculations were used to study the adsorption of three transition metal atoms (Fe, Co, and Ni) on the external surface of two zigzag and two armchair graphyne nanotubes. The most stable position for the adsorption of all three metal atoms on all nanotubes is on the acetylenic ring. The metal atom remains in the plane of the acetylenic ring and makes six bonds with neighboring carbon atoms. Fe and Co complexes are magnetic and show different properties such as metal, semimetal, half-semimetal, and half-semiconductor. Ni complexes are nonmagnetic and semiconductive, with a narrower bandgap in comparison to bare tubes. The results of these calculations are relevant for spintronics and the design of future electronic devices.