What can I do if I find my music online illegally?

Depending on where exactly you have found your music online there are various things you can do to have it removed.

You can issue a DMCA takedown notice which is an official letter to remove copyright material from the internet that is being unlawfully distributed. In order to issue a DMCA takedown you need to submit a written notification by a person authorized to act for the copyright/license holder.

• Contact information (including address, phone number, and email).
• The full name of the track/release in question.
• The web address of the track/release in question.
• A statement of good faith belief that use of the material in question is not authorized by the copyright owner, its agent, or the law.
• A statement that the information in the statement/notification is accurate.
• A statement that, under penalty of perjury, the legal entity is authorized to act for the copyright holder.
• Signature (written or electronic).

If you find links to file storage sites like rapidshare.com or yousendit.com then the best course of action is to contact the file storage sites themselves and submit an email via their instructions which detail the copyright infringement. In most cases, they will remove your content in 24-48 hours. Once they have done this then all links that were offering this file for download will now be broken. 

Most file storage, search engines sites etc. have a contact us / abuse section which explains how to submit your copyright infringement email.

You can also report videos on Youtube, posts on Facebook etc.

If all of this does become very time consuming though, so you may want to consider using a paid service such as Audio Lock.