Extraer string con expresiones regulares

Dim rgx As New Regex("GO")
Dim j As Long = rgx.Match(sp).Index ' donde inicia
Dim fin As Long = string.Length
Dim match As Match = rgx.Match(string)
If match.Success Then
Dim i As Integer = match.Index
Dim st As String = string.Substring(i, fin - i)
End If