Nested Ifs Or Select Case?

hi 

in my form i have 13 textbox (txt1,txt2,....text13) as parameters to search data from my database sheet.

i need to check availability of 13 textbox.value  to find how many of them have value to search my data based on their values by clicking search button.

may all textboxes have value or just one of them or non of them it not matter.

i looking for a statement of using  nested if or select case for this issue.

pls let me have your good Idea

Nima