That's just factually incorrect. Celebrity endorsements are actually more powerful now than in the past, I'm assuming because youtube style celebrity makes it seem more like the persona the celebrity presents is an actual person, or just more exposure though those explanations are just my handwave. https://www.nielsen.com/content/dam/nielsenglobal/apac/docs/...

Someone's random article from a non-ranked journal, but looks like it's got some decent reference papers http://www.jimsjournal.org/13%20Yi%20Ching%20Tsai.pdf