Area effect spells generally don't involve attack rolls.
This might be why you're having a hard time finding it. 4e has got you used to making attacks against all targets in an AoE; but 5e doesn't work that way, and therefore doesn't tell you to do that anywhere. (It also doesn't say not to, but naturally it can't include every possible negative instruction.)
Individual spells will say so when they require an attack roll. Mostly this is for ranged, single-target effects (though AoEs that can go "wide" from where you wanted them to land could conceivably call for a single attack roll for placement). For the AoE itself, instead of individual attacks made by you, generally the spell will say that the targets caught by the AoE make saving throws to avoid or mitigate the effect.
As a rule of thumb, only one side rolls: either you, or the targets. You'll notice that when attack rolls are called for, targets aren't given saves; when saving throws are called for, you don't also roll to see if you hit.