Honestly i have tried different ways.
I have acted friendly and asked them to work as a team. Didn't work.
I took the lead, using chat/pings for a great teamwork, this did work but highly depends on maturity of your team and if they haven't give up yet.
Trolling, works all time but can get you banned
Starting surrender, doesn't work, even in the games with a teamscore of 0/30 they still think they can win and will report you for negative altitude (spellt wrong)
Flaming, works a few times, fun to do and will lose my stress, i mostly flame 1 specific person and then my team agrees with that this user fked it for all of us, even though we still lose it will end in a very good game which wasn't a waste of time