Nike #MakeItCount in 2012 (Twitter)
The goals of the campaign were to use the Nike brand to encourage and motivate people to "make it count" this year. The campaign focused on fitness and health and incorporating powerful photos, content, and videos corresponding with the "make it count" message. The campaign was cross-channel (Instagram, YouTube, Twitter, Facebook); however, the hashtag was the stickiest aspect of the program.
Here's how the campaign was implemented on Twitter:

The #MakeItCount campaign was launched in January 2012, right around the time when people are checking in on their New Year's resolutions. The campaign features 11 athletes in three countries. Videos, photos, and links about how these 11 athletes were pushing their boundaries and "making it count" were shared on social channels using the #MakeItCount hashtag. This content was shared virally, and users began sharing their own #MakeItCount experiences and how they were motivating and pushing themselves.
Why this was one of the best social media campaigns of 2012:
The campaign was in-line with Nike's core messaging: "Just Do It." Choosing 11 athletes and leveraging their fans and followers amplified the messages. The #MakeItCount hashtag was brilliantly crafted to be succinct, to-the-point, relevant, and easily shareable. Furthermore, the videos are highly engaging and motivational.
Source: The Inspiration Room