Check if listbox contains textbox

Check if listbox contains textbox

I know I could use .FindString for this but for some reason it is not
working.
Basically,if listbox items contains just a PART of textbox text,it does
action.
Here's the example of not-working code :
Dim x As Integer = -1
x = ListBox1.FindString(TextBox1.Text)
If x > -1 Then
'dont add
ListBox2.Items.Add("String found at " & x.ToString)
Else
End If