Hi,
Please use below code.
Code
public void SearchFolder(string folderName)
{
    DriveInfo[] allDrives = DriveInfo.GetDrives();
    FileInfo[] files = null;
    foreach (DriveInfo dir in allDrives)
    {
        if (dir.IsReady)
        {
            DirectoryInfo dirInfo = new DirectoryInfo(dir.Name);
            files = dirInfo.GetFiles(folderName + "*.*", SearchOption.AllDirectories);
        }
    }
    List<string> fileNames = new List<string>();
    foreach (FileInfo file in files)
    {
        fileNames.Add(file.Name);
    }
}
I hope this will help you out.