Regex is what you need
Code:
Dim data As String
data = "this is a first line_this is a second line_this is third"
Dim lines() As String
lines = Regex.Split("_", data)
lines(0) will be "this is a first line"
lines(1)will be "this is a second line"
lines(2) will be"this is third"
Check this
link