A game can be resigned at any time, even if it's not your move.
But for resigning a multi-player-game, you normally should have the consent of your team-members, though it's not enforced by DGS.
 
By official rules in Rengo, the current player wanting to resign, is inclined to ask the team-partner if it is ok with the phrase "May I resign?", on which the partner may answer with only "Yes" or "No".
 
DGS is not enforcing this rule, but clicking "Resign" on the game-page shows a note with a link to send a bulk-message to the other players of the same team to ask if it's ok to resign. But this lies in the discretion of the player to move. The link leads to showing a preview of a bulk-message to the correct team-players with a link to the game.
 
For Rengo it's pretty clear (only one answer is to be expected), but for other MP-games with more than two players in the same team, there might appear both answers (Yes & No). The interpretation of that is left to decide for the one who asked.
 
If you are not using official rules, you may adjust the text and send that instead. But ensure, you keep the important information in there (reference to the game and the question to resign).
After your team mates have answered per private message, you may go on with submitting the resignation.
 
However, asking for resignation is not enforced, so you can resign regardless of asking your team-mates.