How to split one big text file into multiple files in powershell

Hello I have one big text file like this

BIGFILE.TXT

COLUMN1,COLUMN2,COLUMN3,COLUMN4,COLUMN5,COLUMN6,COLUMN7,COLUMN8     # HEADER
11/24/2013,50.67,51.22,50.67,51.12,17,0,FILE1
11/25/2013,51.34,51.91,51.09,51.87,23,0,FILE1
12/30/2013,51.76,51.82,50.86,51.15,13,0,FILE1
12/31/2013,51.15,51.33,50.45,50.76,18,0,FILE1
1/1/2014,50.92,51.58,50.84,51.1,19,0,FILE2
1/4/2014,51.39,51.46,50.95,51.21,14,0,FILE2
1/7/2014,51.08,51.2,49.84,50.05,35,0,FILE2
1/8/2014,50.14,50.94,50.01,50.78,100,0,FILE3
1/11/2014,50.63,51.41,50.52,51.3,190,0,FILE3
1/15/2014,54.03,55.74,53.69,54.93,110,0,FILE4
1/19/2014,53.67,54.19,53.55,53.82,24,0,FILE4
1/20/2014,53.83,54.26,53.47,53.53,23,0,FILE4
1/21/2014,53.8,54.55,53.7,54.1,24,0,FILE4
1/26/2014,53.26,53.93,53.23,53.65,31,0,FILE5
1/27/2014,53.78,54,53.64,53.81,110,0,FILE5

I'm looking for way how to split this file into multiple text files.
In this case one file would be split into 5 text files. Name of each
text file would be taken from column number 8. The big file is comma
delimited. So the output would be:

FILE1.txt

COLUMN1,COLUMN2,COLUMN3,COLUMN4,COLUMN5,COLUMN6,COLUMN7,COLUMN8   # HEADER
11/24/2013,50.67,51.22,50.67,51.12,17,0,FILE1
11/25/2013,51.34,51.91,51.09,51.87,23,0,FILE1
12/30/2013,51.76,51.82,50.86,51.15,13,0,FILE1
12/31/2013,51.15,51.33,50.45,50.76,18,0,FILE1

FILE2.TXT

COLUMN1,COLUMN2,COLUMN3,COLUMN4,COLUMN5,COLUMN6,COLUMN7,COLUMN8   # HEADER
1/1/2014,50.92,51.58,50.84,51.1,19,0,FILE2
1/4/2014,51.39,51.46,50.95,51.21,14,0,FILE2
1/7/2014,51.08,51.2,49.84,50.05,35,0,FILE2

FILE3.TXT

COLUMN1,COLUMN2,COLUMN3,COLUMN4,COLUMN5,COLUMN6,COLUMN7,COLUMN8   # HEADER
1/8/2014,50.14,50.94,50.01,50.78,100,0,FILE3
1/11/2014,50.63,51.41,50.52,51.3,190,0,FILE3
.
.
The "big file" has more than 250 000 lines.. And the output should have more than 1000 small files. So I'm 
looking for a way how to generate more than 1000 small files 
automaticly. The file name for all small files is always stored in 
column #8.
One good soul already helped  me with a code:                    
                    

$src = "c:tempreallybig.csv"  # Source file
$dst = "c:tempfile{0}.csv"    # Output file(s)
$reader = new-object IO.StreamReader($src)  # Reader for input

while(($line = $reader.ReadLine()) -ne $null){ # Loop the input
    $match = [regex]::match($line, "(?i)file(d)") # Look for row that ends with file-and-number

    if($match.Success){
     # Add the line to respective output file. SLOW! 
     add-content $($dst -f $match.Groups[0].value) $line 
    }
}
$reader.Close() # Close the input file                            

But there should be made 3 small (?) changes to the code to work exactly how I need.