How to play Support with a split team.

I love to play Sona and other supports but I feel unable to help when all my team is split. Mid trying to gank in enemy territory, adc overextending into enemy territory, jungle feeding top and top who knows... As a support what should I do? I cannot follow/help anybody when they try to engage fights 2 vs. 5. They refuse to group or play under turret with a negative score. So, what to do?
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