How can I get a list of AD groups that match a partial name?

I need to search AD for any groups that match a partial name, then search each group for the users inside it.

I have the code to list the users in a group, listed below.  But how do I get the listing of the groups to search?

Public Function UsersInActiveDirectoryGroup(ByVal GroupName As String) As Specialized.StringCollection
   Dim members As New Specialized.StringCollection

   Try
       Dim domainContext As New ActiveDirectory.DirectoryContext(ActiveDirectory.DirectoryContextType.Domain)
       Using dc As ActiveDirectory.DomainController = ActiveDirectory.DomainController.FindOne(domainContext)
           Using pctx As New PrincipalContext(ContextType.Domain, dc.Domain.Name)
                Using grp As GroupPrincipal = GroupPrincipal.FindByIdentity(pctx, IdentityType.Name, GroupName)
                    If Not IsNothing(grp) Then
                        For Each p As Principal In grp.GetMembers(True)
                             members.Add(p.SamAccountName)
                        Next
                     End If
                 End Using
             End Using
         End Using
         Return members
     Catch ex As Exception
         Return Nothing
     End Try
 End Function