Enter Find Mode [ no pause ]
Set Field [ table::yourDate ; Month(get(currentdate)) & "/*/" & Year(get(currentdate)) ]
Basically you are calculating the current month, EG today is 12/12/2015 so this would return 12/*/2015. The * is a search variable allowing any value for the month.
Using filemaker's date functions will allow you to set date searches dynamically. I also like the above rather than trying to throw your requests in the perform find script step because it's easier to read. In this case the perform find script step is the equivalent to the return key or pressing the "perform find" button while you are in find mode.
Mike B's answer is correct, and may be easier to understand when you review the code later.
A shortcut is simply to use:
Set Field [ table::yourDate ; Month ( Get ( CurrentDate )) ]
If you put just the month in a date field when you search, FileMaker automatically assumes you want any day in that month in the current year.