Do you think art work need(s) to be seen by many to be effective?
Does art work have to communicate a message to be effective?
In answer to your first question, no, it only has to be seen by the artist to be effective. I have several works I've done purely for myself which I would NEVER show to anyone. They are SO private I plan to destroy them before I die.
In answer to the second question, with the exception of the instance sited above, I feel the answer is YES. At the most basic level, art is creative communication, and when it ceases to communicate then it becomes merely self-indulgent drivel. Of course, communication, as we are accustomed to defining it, demands the artist and the viewer both be speaking the same language, and if that is not the case, then the fault does not lie with the artist but with the viewer, except, as mentioned above, when the artist is speaking a language NO ONE else understands, in which case, the drivel label applies.
I could never understand Japanese poetry for example, but that does not make it any less artful. The fault for this "failure to communicate is MINE, not that of the Japanese poet. Thus, there is EASY art, such as Norman Rockwell, and HARD art such as Mark Rothko. Rockwell painted in the vernacular. Rothko painted in a language understood by less than one tenth of one percent of those viewing his works. To be understood, like the Japanese poet, he demanded that the viewer learn to speak his language. However, beyond that, (at least in Rothko's case) creative communication was not so much literal as visceral. His massive black strokes on white canvas were not to be "read" but "felt". Interpolating back therefore, perhaps I need not "understand" Japanese poetry, but merely enjoy the "feel" of it--the harmonious flow of it's sounds--to appreciate it as art.