I think your best bet is to import all data from all text files, into one single sheet, and then filter for the strings you want to find, and copy/paste those to another sheet.
Try the script below to import all data from all files.
Sub ImportCSVsWithReference()
'UpdatebyKutoolsforExcel20151214
    Dim xSht  As Worksheet
    Dim xWb As Workbook
    Dim xStrPath As String
    Dim xFileDialog As FileDialog
    Dim xFile As String
    On Error GoTo ErrHandler
    Set xFileDialog = Application.FileDialog(msoFileDialogFolderPicker)
    xFileDialog.AllowMultiSelect = False
    xFileDialog.Title = "Select a folder [Kutools for Excel]"
    If xFileDialog.Show = -1 Then
        xStrPath = xFileDialog.SelectedItems(1)
    End If
    If xStrPath = "" Then Exit Sub
    Set xSht = ThisWorkbook.ActiveSheet
    If MsgBox("Clear the existing sheet before importing?", vbYesNo, "Kutools for Excel") = vbYes Then xSht.UsedRange.Clear
    Application.ScreenUpdating = False
    xFile = Dir(xStrPath & "\" & "*.txt")
    Do While xFile <> ""
        Set xWb = Workbooks.Open(xStrPath & "\" & xFile)
        Columns(1).Insert xlShiftToRight
        Columns(1).SpecialCells(xlBlanks).Value = ActiveSheet.Name
        ActiveSheet.UsedRange.Copy xSht.Range("A" & Rows.Count).End(xlUp).Offset(1)
        xWb.Close False
        xFile = Dir
    Loop
    Application.ScreenUpdating = True
    Exit Sub
ErrHandler:
    MsgBox "no files csv", , "Kutools for Excel"
End Sub
Then, run this.
Sub MoveData()
With Application
.ScreenUpdating = False
.EnableEvents = False
End With
Dim Rng As Range
Set Rng = Range([A1], Range("A" & Rows.Count).End(xlUp))
On Error Resume Next
With Rng
.AutoFilter , field:=1, Criteria1:="Book1"
.SpecialCells(xlCellTypeVisible).EntireRow.Copy Sheets("Sheet2").Range("A1")
.AutoFilter
End With
Application.EnableEvents = True
End Sub