I took a look at the size of the typeface (font) used on Face Book and it appears they are going with a 13-pixel size.
There are a lot of arguments by web designers about using bigger and bigger typefaces on websites but iconic Facebook sticks with the rather small 13px size and they get millions and millions of views on their site each day.
So, not to be outdone, I have now installed 13px on this very site. Guess what? — I can read it with little or no difficulty and if I did have problems reading it, I could always invoke the “Zoom” function of my computer monitor. (Right now my zoom is set at 100%. I used to set it at 110% and even 125% but recently I have been satisfied with 100% for everything, including my own blog.
I do not get millions of hits on my blog each day but some days (most days) I seem to hover in the range of 700 to 1,000 and sometimes a little more or less … and I am happy with that for the time being. It does take some time to build an audience and so far, I have been blogging right here on this site and over at Blogger for a little more than 7 years now.