Hashtags are one of the most effective organic ways to increase brands reach to connect with large audience group. You can use hashtags to target specific user groups. You can use Trackmyhashtag - it is an effective twitter hashtag and event tracking tool that provides real time performance metrics.
Trackmyhashtag provides such as - Total tweets, reach, impression, tweet timeline, most popular tweets, related trending hashtags and media, and other useful metrics.
I hope this helps!