Consult a qualified lawyer–especially if this is a matter of serious concern for you, or money is involved. A lawyer who is versed in copyright law is the best source of information about the extent of your rights, and whether you may be able to recover any damages for the infringement.
If you do not have the inclination or the means to consult a lawyer, and you choose to go it alone, you certainly can. If you\’re a designer who needs assistance collecting information about an infringement and you turn to your readers and customers for help (which can be done successfully), make sure that you provide enough information and precise instructions so that your faithful customers and fans don\’t embark on a witch hunt or start harassing properly licensed users of your work. It is definitely not advisable, though, to post a public notice accusing another party of infringing your work. What if it turns out not to be true? Allegations like that can be actionable as false and misleading statements, trade libel, or defamation of character.