@erinjo perhaps the difficulty in creating an effective icon stems from the fact that the physical metaphors associated with “share” do not map well to the online behaviour associated with the term, allowing the word to be used successfully but making giving it an image a challenge.
My theory: the most basic usage of “share” generally refers to organising mutual access to some resource between pre-determined, consenting participants (he shared his food with him, she shared her connection with her coworkers, the schools shared a playing field). This holds for more abstract non-physical use of “share”, as in “she shared her story”, ”they shared a secret”.
In some cases (e.g. private messaging [where the verb “message” or “send” would more often be used] or posting to a group) the “known participants” facet holds up, but not so much the pre-determination and/or mutual consent/awareness present in the physical examples — unless for example the context is an online group set up explicitly for the sharing of links to resources about a topic.
In the common case of “sharing” as it’s characterised online (posting a short text post containing a link and optionally some comment, typically with a link preview, broadcast to a wide audience on a whim with no mutual pre-determination), not much of the original metaphor holds up, and I’d argue that “post” is a more suitable term (“publish” less so as its use connotes posting of a thought-out original work).
None of this is backed up by actual data though — I’d be interested to hear your thoughts on it.