procedure TForm1.Button1Click(Sender: TObject);
var
  search: string;
begin
  search := 'mali';
  if SendMessage(ListBox1.Handle, lb_selectstring, - 1, Longint(PChar(search))) <> LB_ERR then
    ShowMessage('Bulunulanlar: ' + IntToStr(ListBox1.ItemIndex));
end;