how can I write a search text in richtextbox?

Thank you!
no, my program is application that work in network, and crawl in html code and find links. so i have request / response we page. now my response is in rich text box. now i want saerch any word for example ( html, ).
i want a search like search in notepad.

my code is here.

public partial class Form1 : Form
{
int start = 0;
int indexOfSearchText = 0;

public int FindText(string txtToSearch, int searchStart, int searchEnd)
{

if (searchStart > 0 && searchEnd > 0 && indexOfSearchText >= 0)
{
XSSResponceRichTextBox.Undo();
}

int retVal = -1;

if (searchStart >= 0 && indexOfSearchText >= 0)
{

if (searchEnd > searchStart || searchEnd == -1)
{

indexOfSearchText = XSSResponceRichTextBox.Find(txtToSearch, searchStart, searchEnd, RichTextBoxFinds.None);

if (indexOfSearchText != -1)
{
retVal = indexOfSearchText;
}

// if (indexOfSearchText == -1)
else
{
searchStart = 0;
indexOfSearchText = XSSResponceRichTextBox.Find(txtToSearch, searchStart, searchEnd, RichTextBoxFinds.None);
retVal = indexOfSearchText;
}

//if (indexOfSearchText == -1)
//{
// searchStart = 0;
// indexOfSearchText =XSSResponceRichTextBox.Find(txtToSearch, searchStart, searchEnd, System.Windows.Forms.RichTextBoxFinds.None);
// retVal = indexOfSearchText;
//}
}
}

return retVal;
}

public Form1()
{
InitializeComponent();
}

private void txtSearch_TextChanged(object sender, EventArgs e)
{
if (start != 0)
{
XSSResponceRichTextBox.Undo();
start = 0;
indexOfSearchText = 0;
}
}



private void txtSearch_KeyPress(object sender, KeyPressEventArgs e)
{
int startindex = 0;

if (e.KeyChar == ">

My code can not run to my application.