Using Textbox To Deal With String More Efficiently?

I've been trying to improve the efficiency of my giant program and I know that using a textbox to deal with a string is terribly inefficient.
Function CollectionSplit(ByVal TheString As String, ByVal TheSeperator As String)
Dim tb As New TextBox
tb.Text = TheString.Replace(TheSeperator, Environment.NewLine)
Dim returnable As New Collection
For Each x As String In tb.Lines
If Not x.Length = 0 Then returnable.Add(x)
Next
Return returnable
End Function
What it does is convert a string of "1,2,3" into a collection of the 3 separate items for use later on.