We don't know how your company is run, but this could be a way to get yourself into trouble, and/or make your users hate you. As others stated, the best way to prevent that stuff is to block p2p traffic. File types are not illegal per se.
However, if you are sure you want to do this and are allowed to, the best way would be to use a simple Powershell Script.
This one will not give you beautiful results, but it will give you a starting point. It will save the Output in a .txt File on the user's computer.
# * Make an array of Computers you want to check
$ComputerNames = "PC1","PC2","PC3"
# * Define the path you want to check there
$Path = "C:\Users\"
# * Loop through your List of PCs
Foreach ($Computer in $ComputerNames) {
# * Invoke Command on every PC in List
Invoke-Command -ComputerName $Computer {
# * Get the Files you search for and write them in a text file.
Get-Childitem -Path $Path -File -Recurse|Where-Object {$_.Extension -eq ".mp3" -Or $_.Extension -eq ".avi" -Or $_.Extension -eq ".tor"}|Select-Object FullName > C:\Output.txt
}
}