A persuasive essay is different from an argumentative essay in a way that, when you try to persuade the reader, you may rely not only on facts and evidence (which you would normally do with an argumentative essay), but also on emotional appeals to the reader. So, when writing a persuasive essay, evidence like "80% of whales wander ashore because of human-caused ocean pollution" is just as valid for your essay as "Can you imagine what a horrible death a whale suffers, suffocating on the shore?" Persuasion is about strong opinion and evidence.
The structure of the essay is standard, as, for instance, it is suggested in high school book report template: introduction, body paragraphs and conclusion. The introductory statement must explain the importance and controversy of the topic given. This importance can be conveyed by means of a "hook" first sentence, which will immediately grasp the attention of the reader. For example, "Imagine empty oceans, with no underwater life". Your reader will instantly envision the problem and thus be compelled to continue reading. At the end of the introductory part, your view must be clearly given. The conclusion of a persuasive essay must briefly restate your view and main arguments that support it once more, and give predictions about the future development of the subject area.