The key thing to remember for single product launch is to use the designated hashtag in every post, retweet, and report on every social property that has to do with that product over the course of the campaign so you can measure its effectiveness. Through shareability, tagging, and User Generated Content (UGC) you are able to gauge general interest, adoption and satisfaction levels. Then compare it to your sales over a specific period with social engagement, and thus track and determine your social ROI.
A good example of successful brand affinity campaign is @thenorthface, putting a designated hashtag in their 'about us' section on Twitter is interesting, as it lets the public know what hashtag to use when talking about them #neverstopexploring. This encourages customers to share personal stories and experiences with the brand while weaving its essence into their lives, amplifying the brand in the process. By empowering customer engagement though UGC, you by default create a living, searchable storyboard of relevant brand experiences.
Drawing your attention to a more current trending topic is the 2014 FIFA World Cup and Adidas campaign #allin. The brand cleverly designated the #allin hashtag and used it across their marketing content with a clear focus on Twitter. Adidas gives their fans the opportunity to participate in two ways: either follow the conversation as it is evolving on Twitter or all in with email and they'll send you the very best FIFA World Cup 2014 content direct to your inbox. They also created a microsite to attract fans to the campaign and to engage with their brand.
In a perfect world your fans and followers will know the appropriate hashtag to use when posting relevant content. But you can't count on that in the beginning. This happens through creativity, active community engagement, and positive conditioning. Customers are going to share experiences. It's more effective though when you give them something to #talkabout in a way that tells meaningful stories with each update and as an overall storyboard.