Also, because the words are shouted I think the idea of "suddenly" is implicit, although you could include the word for emphasis ("Mike suddenly shouted in a shrill voice...").
You might even be able to say "Mike screeched, 'Look everybody!'" because screech means to shout or cry out in a shrill voice.
If you are writing for a test, I'd probably use one of my options above or something similar. If you are writing your own work of fiction, you'll probably have more creative latitude. (Please note that my usage of single and double quotation marks is standard in U.S. English, but if you are writing in British English, they would be inverted. Also, in your writing, you would only be using one pair of quotation marks, so in that case, just use double quotation marks for the speech if you are writing in U.S English and single quotation marks if you are writing in British English.)