Try this:-
Imports System.IO
Module Module1
Sub Main()
Dim path As String = "D:\New folder"
Dim di As New DirectoryInfo(path)
Dim yourSearchString As String
yourSearchString = "to"
Console.WriteLine("Match Found:-")
For Each fi As FileInfo In di.GetFiles()
If File.ReadAllText(fi.FullName).Contains(yourSearchString) Then
Console.WriteLine(fi.Name)
End If
Next
End Sub
End Module
I hope this will help you..