Hayden Panettiere Fans Slyly Plaster Neutrogena's IG Account With Tributes

Neutrogena continues to get lit up by Hayden Panettiere fans ... and now the skincare company's Instagram is being turned into a shrine of sorts.

Here's the deal ... Hayden was the face of the brand for years before being unceremoniously dropped, allegedly because she made public comments about her postpartum depression ... and after her shocking death, fans have their claws out -- calling for a boycott.

Beyond inundating Neutrogena IG posts with venomous comments about Hayden's treatment -- fans have been leaving under-the-radar tributes and shaming the brand on the clearly unmonitored -- and often forgotten about -- "Tagged" section of its IG page.

TMZ discovered numerous posts under the tags section ... ya know, the one where people tag the folks or brands who are in their photos.

The tags section can also be a haven for trolls and hate mail ... and that's the case here.

The section can be turned off -- or moderated so only positive comments are approved -- which is clearly not happening on Neutrogena's page ... at least not yet.

Seems someone is asleep at the wheel ... or they're just letting their haters pop off.

We've reached out to Kenvue, Neutrogena's parent company, for comment ... so far, no word back.