highlight every found string in a richtextbox C#

[jason]

Hello - I have this simple code that highlights THE FIRST string found,
but NOT ALL strings in the richtextbox. Can anybody suggest an easy way
to hightlight all strings (caseless as well) in the richtxtbox? If you
have a regex example that would be even better.
private void toolStripMenuItem2_Click(object sender, EventArgs e)
{
int x;
x = richTextBox1.Find(textBox1.Text);
richTextBox1.SelectionStart = x;
richTextBox1.SelectionLength = textBox1.Text.Length;
richTextBox1.SelectionBackColor = Color.YellowGreen;
}