You're actually obligated by TOS to try your best to win every game and stay till the bitter end, regardless of what your teammates are doing. The report button at the end of the game exists -- report teammates who intentionally feed.
Learn the difference between "intentionally feeding", "being mechanically bad at the game", "playing a champion you aren't familiar with", "playing an off meta pick", "being in a bad matchup", "being camped", "making bad strategic decisions" and "i'm already 0/10 so this wave i'm overextending for is worth more gold than me". In most cases, unless they're actually running it down, building AP Garen, or following the jungler around the jungle stealing their camps when they're standing there fighting them, they aren't inting.
A 17/1/10 Akali who rages at you for taking her red buff and runs it down mid once before going back to killing everyone to pay you back for taking the red buff is intentionally feeding.
A 0/10/0 Caitlyn who has been overextending for farm since 0/5 is not intentionally feeding.
Overextending for farm isn't intentional feeding.
Taking a 1% play isn't intentional feeding.
Missing a flash over a wall isn't intentional feeding.
Missing skillshots isn't intentional feeding.
Using abilities in the wrong order isn't intentional feeding.
Making a bad strategic decision isn't intentional feeding.
Building suboptimally isn't intentional feeding.
In fact, attempting to surrender a game is by definition intentionally trying to lose and has a higher chance of losing your team the game than any action you can take on Summoner's Rift. 100% of all surrendered games have ended in a loss for the surrendering team, without a single exception in the entire history of League of Legends. This includes all levels of play from the depths of level 1 games to the World Finals, in every single region, every single patch, regardless of what champions are on the map or who's playing them, what the score is, or any other factor. Even if you took the full roster of Invictus or Fnatic or Team Liquid and pitted them against brand new level 1 players who've never seen a MOBA before, if the pros do /surrender, they will lose 100% of the time. It doesn't matter that they're the best players in the world or that they're 30k gold up or that their opponents don't know what the controls do, if they type /surrender they will lose.
No. If you're "being held hostage", you play your best and report people who are actually inting in the postgame lobby.