After spending six seasons in the KHL, Plotnikov singed a one-year, entry-level contract with the Penguins last summer, however the Russian has struggled in his first NHL season registering just two assists in 32 games and has not played since Jan. 6.
Plotnikov, 25, becomes a restricted free agent on July 1.
The Penguins are preparing for a playoff run, while the Coyotes are looking towards next season. Pittsburgh acquired defenceman Justin Schultz from the Oilers Saturday.
Plachta, 24, is also set to become an RFA after the season. In 46 games with the AHL’s Springfield Falcons the German winger has two goals and five assists.