Puyo Puyo Tetris was released in 2014, so I'm not sure that many people still play online there. Puyo Puyo Tetris 2 was released for PC very recently, but there are large complaints from many of the Tetris pros due to decreased DAS speed and the ridiculous combo table. If you really wanted to play Puyo Puyo Tetris, I would suggest buying Puyo Puyo Tetris 2 since it's basically an improved version of the old game. However, if you want to play on a game with a large community, I would suggested Tetris Effect: Connected (40$ available on PC and console), TETR.IO or Jstris (both free to play browser games). These games have a much more active player base with the professionals playing than compared to Puyo Puyo Tetris.
TLDR; get Puyo Puyo Tetris 2 if you want to, otherwise play TE:C, TETRIO, or Jstris