Despite its scale — at about 100 million monthly users — Twitter has posted meager revenue, which came to an estimated $140 million in 2011 (according to eMarketer). Consider that during the same period Facebook generated $3.15 in revenue.

But with a valuation of about $8.4 billion, Twitter realizes it needs to get serious about its business model. To help things out, the company has teamed up with American Express (NYSE:AXP) for an interesting promotion. That is, if a card user tweets or retweets certain types of products, he or she will get discounts. It will mean connecting your Twitter account to the American Express system.

American Express has been at the forefront of social media and mobile. For example, the company has a similar deal with Foursquare, which is a location-based service for Apple’s (NASDAQ:AAPL) iPhone and Google’s (NASDAQ:GOOG) Android.

As for Twitter, the partnership with American Express is certainly important — and could lead to some monetization. However, if Twitter wants to substantially boost revenues, it needs to show that it can get major brands to pay for sponsorships. And so far, this hasn’t been easy.