How to find Malicious Plugin

I made a website and used few plugins but since it is up someone is entering and making changes, uploading articles and corrupting website (deleting index.php) resulting website is getting stopped.

Please help how to find malicious plugin which is letting them enter into the website.

Maybe it’s not a plugin but something else, like someone who knows your sftp password. Check your access logs and make sure that the only successful accesses are from IP addresses you know, own or recognize. Once that is out of the question, I’d start from scratch with a fresh installation of everything: wordpress code, plugins and themes. Don’t copy anything from the old site, download fresh copies from the original places. If you still have issues, there may be something nasty hiding inside the content of your site’s database… you’ll need to dive deeper at that point and get your hands really dirty (or hire a professional to fix things for you).
Also, consider running a malware scan