Kate contributes $500 on a crowdfunding website (e.g., GoFundMe) to support victims of a recent hurricane. Is the contribution deductible for Kate, and are the proceeds included in gross income for the recipient(s) of the funds?

IMPORTANT: I know the answer to this question--it is not likely to be deductable because the website does not conform to the code's definition of a charitable class.What I DON'T know is how to locate a primary source that confirms this. By primary source I mean legal source--a citation of the relevant Code section, subsection or regulation, or a judicial decision--not an IRS publication.