I highly doubt that Reddit per se has any significant effect whatsoever—which is not to say that it can't be an instance of the overarching platforms that cause the phenomenon.

The reason I'm disregarding Reddit as a significant cause is threefold:

a) Reddit is overwhelmingly male, and the most affected group are teenage girls

b) Reddit is no that big of a platform in the teenage demographic

c) Even if it were, its popularity is not in any way homogeneous across countries. If Reddit itself had an effect, the USA would be much more affected by the phenomenon than the UK, for instance.