This is my working query:

Query = "select Cust_Id, Card_Number, Clients_Title, Address_Current, Phone_Number, Mobile_Number from Customer_New Where 1=1";
try
{
    if (txt_title.Text != "")
        Query += " and Clients_Title Like '%" + txt_title.Text + "%'";
    if (txt_address.Text != "")
        Query += " and Address_Current Like '%" + txt_address.Text + "%'";
    if (txt_phone.Text != "")
        Query += " and Phone_Number Like '%" + txt_phone.Text + "%'";
    if (txt_mobile.Text != "")
        Query += " and Mobile_Number Like '%" + txt_mobile.Text + "%'";
    if (cbo_location.Text != "")
        Query += " and AreaLocation Like '%" + cbo_location.Text + "%'";
}

catch { }

Here I am attempting to write its equivalent SQL case Expression.

SELECT Cust_Id, Clients_Title, Card_Number, Key_Person, Address_Current, Phone_Number, Mobile_Number, AreaLocation
FROM Customer_New
    WHERE  1 = CASE WHEN @Clients_Title != " " THEN Clients_Title AND
                    WHEN @Address_Current != " " THEN  Address_Current AND
                    WHEN @Phone_Number != " " THEN Phone_Number AND
                    WHEN @Mobile_Number != " " THEN Mobile_Number AND
                    WHEN @AreaLocation != " " THEN AreaLocation
               END 

Can any one correct my case expression?