https://blog.hollywoodbranded.com/the-power-of-influence-in-...

I'm guessing here, because as the sentence is written, there is no apparent connection between the two parts. The sentence lacks meaning. If we think about it, the reason those influencers become so, well, influential is that Gen Z spend so much time on platforms with influencers, compared to platforms with blogs. In any case, this is not what the sentence says in a literal sense.

It's a strange use of plébisciter to be sure, and the whole sentence is clumsy, but one meaning that makes sense to me in the context is that these social media have become wildly popular with youngsters at the expense of blogging and other platforms.

In the beginning of the Web, forums were cool but noncommercial (they still are among oldies or specific communities like this one). When blogging came along, some people earned a (meagre to good) living by punting this or that company (many still do this). But now the real action is on YouTube and Instagram where top influencers (there's another word along with selfie that I hope does not survive the apocalypse) do very well for themselves and a tiny few are (multi)millionaires.

So I think the idea behind plébisciter here is that kids are voting with their fingers and eyeballs, so to speak, and are totally immersed in these social media.

or if you want to put less kindly, but more literally:

"when it comes to getting approval from Youtube, .... plebeians (/crowds /users ....)

HERE "Youtube" is a shorthand for "Youtube users", same as very often "The Internet" is used to mean "PEOPLE using the Internet", instead of the literal meaning for "The Internet" = a huge pile of networked HARDWARE and SOFTWARE.

step one: what is a most literal plébiscite:

Plébiscite

Un plébiscite (du latin plebiscitum — de plebs, « plèbe, peuple », et scitum, « décision, décret ») est une consultation sur le désir d'une population à propos d'une importante décision, comme celle de relever d'un État ou d'un autre. Au sens latin du terme, le plébiscite est conçu comme un instrument véritablement démocratique, et non comme celui du césarisme1.
....
https://fr.wikipedia.org/wiki/Plébiscite

IOW it's a vote by the whole population to approve or not some proposal.

Step two: what it could mean in this ST

so the verb "plébisciter" would mean seeking the mass approval for some idea / proposition [soumettre une proposition au plébiscite (=au vote direct par l'ensemble de la population] OR someone getting massive support (se faire plébisciter), depending on the sentence.

What makes sense in in this ST is:

when it comes to getting [mass] approval from Youtube, .... audiences (/users)

I'll try to avoid "la preuve par l'absurde" as being too easy.

"Ils utilisent en moyenne 5 plateformes sociales par jour ! Cette génération donne toute-puissance aux influenceurs versus les blogueurs quand il s’agit de plébisciter Youtube, Snapchat, Instagram ou Tik Tok.

Cette génération donne toute-puissance aux influenceurs
=>
"les influenceurs" are those who have an influence on social media users - are in position to make social media users change their mind about whatever is the object of the "influence" they are exercising - some product, some ideas, whatever.

IOW "les influenceurs" make them symbolically "vote for" whatever "les influenceurs" are peddling - and because this category of users is exposed 4 hours per day to "influencers", it gives them (the influencers, not these users) "une toute-puissance" (overwhelming power over users?)

As Youtube, Snapchat, Instagram ou Tik Tok. have massive user bases, if influencers are successful, it's potentially a "massive vote / vote by the masses" (see definition of "plébiscite" ...)

101% sure of the meaning, and find it rather obvious. Basics of the trade for any spin-doctor, BTW ...









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Note added at 3 hrs (2020-03-02 23:26:29 GMT)
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... if influencers are successful, it's potentially a "massive vote / vote by the masses" for whatever they are pushing that they can achieve (see now the definition of "plébiscite" ...)

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Note added at 4 hrs (2020-03-03 01:12:12 GMT)
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another way of dissecting this sentence:

Cette génération donne toute-puissance aux influenceurs versus les blogueurs quand il s’agit de plébisciter Youtube, Snapchat, Instagram ou Tik Tok.
=
if you want to obtain a massive YES vote(/approval /support) [from the Generation Z] through their favorite social networks (Youtube etc) for whatever products or ideas you are pushing, don't bother with bloggers, for this target audience the real impact can be achieved through "influencers" operating on these social networks, as this generation Z has allowed these "influencers" to have huge influence on them.

French term (edited): quand il s’agit de plébisciter Youtube ...

You've parsed it wrongly. This is saying that if one takes a straw poll (or possibly even a real poll) of Youtube, Snapchat, Instagram or Tik Tok users, it will show that influencers have more followers than bloggers.

My suggestion.