Hello, actually, to cheer sb. means: jemanden anfeuern: Die Zuschauer feuerten die Fußballmannschaft mit lauten Jubelrufen an.

Do you mean at a soccer match in the stadion? You can say: "Klasse! Toll! Weiter so! Vorwärts! Schneller! Tor!" There may be more examples.

I can't help with the German, I'm afraid, but may I make a comment about your question? The word you want is 'cheer' , not than 'cheer up'. for example : 'The crowd cheers the players'. 'Cheer up' means to make a sad person feel happier. And good luck with finding your German phrase.