Smartism has no adherent figure, and the absence is not an oversight. The databases that estimate Vaishnava, Shaiva and Shakta populations carry no Smarta line at all, because the category is not one that survey respondents use about themselves and not one with a membership to count. Any number offered here would be invented.
What can be described is influence. Advaita Vedanta, the philosophy Smartism carries, became in the nineteenth and twentieth centuries the form in which Hinduism was presented to the world: by Vivekananda at Chicago in 1893, by Radhakrishnan, and by the neo-Vedanta movements that followed. When a general audience is told that Hinduism holds all religions to be paths to one reality and the many gods to be faces of a formless absolute, it is being told the Smarta position, and being told it as though it were the Hindu position. It is not. Dualist Vaishnava theologians reject it explicitly, and have done so for eight hundred years.
Institutionally the tradition is concentrated in the south (Tamil Nadu, Karnataka, Kerala, Andhra Pradesh and Maharashtra), in the Brahmin communities of those regions and in their very substantial professional diaspora. The Shankaracharyas of the four seats retain real authority, and are consulted and quoted on questions well beyond their own community.
The panchayatana arrangement, meanwhile, has quietly become the ordinary furniture of the Hindu domestic shrine, in a great many households that would not identify as Smarta at all.