This is a US centric answer, but it may apply more widely.
Anything positive you do can be put on a CV, but emphasize more important things and relegate things like this to an "Other" section. They would only be a factor in a graduate school application process in a very minor and marginal way. Your coursework and letters of recommendation are much more important.
But, yes, mention somewhere that you tutor other folk and/or have been awarded a TA position, especially if merit is part of the reason you were give it.
As for Stack Exchange participation, I suggest that you say no more than "Frequent contributor to Math Stack exchange" with a link to the site.
And treat the CV as a living document, pushing lesser things off as more important things are added (published papers, especially).
I have nothing to say about LinkedIn as I don't use it and would be unlikely to visit it as part of a student's application.