Fitoussi, J.P. and K. Velupillai. ("Macroeconomic Perspectives," in H. Barkai, S. Fischer, and N. Liviatan, editors. Monetary Theory and Thought. London:  Macmillan, 1993) agree with Nicholas J. Theocarakis that Frisch is the first to use "macroeconomics," though the Bohm-Bawerk coinage is interestingly close.  But the term took some time to catch on.  

The first JSTOR reference to "macro-economic" and to "micro-economic," both spelled with hyphens is in J.M. Fleming, "The Determination of the Rate of Interest," /Economica /NS 5(19), August 1938, pp. 333-341.  The first reference to both "micro-economics" and "macro-economics" (again hyphenated) is Jacob Marschak, "A Cross Section of Business Cycle Discussion," /American Economic Review/ 35(3), June 1945, pp. 368-381.

It took until 1946 for the term "macroeconomics" (with or without hyphen) to be used 5 times in the JSTOR journals and until 1947 to be used 10 times.  For "microeconomics" the analogous dates are 1947 and 1948.

Kevin Hoover