RichTextBox query

I am trying to write something that will find a word, and highlight it in bold, in some user-entered text.

I am using a richtextbox.

So far I have:

Private Sub Command1_Click()


If InStr(rtbUserText, txtSearchString.Text) Then

rtbUserText.SelText = txtSearchString.Text
rtbUserText.SelBold = True

Else
MsgBox "Word not found"
End If
End Sub

When run, clicking the command button makes the word that is to be found appear on the end of the text in the rtb, but not in bold.

I know that there is something wrong here, but I don't know what! Can anyone help? I just want to highlight the word in bold if it is present, to show that it's been found.

Try finding the start of the word then select it use length...