You have two possibilities of tracking hashtags, depending on your needs.
If you want a real-time status on how many mentions there are using the hashtag that interest you, as a one time analysis, you can use the Quick Research tool.
The tool shows you how many people are mentioning a popular hashtag on web and social platforms, on the market that interest you.
If you want to monitor your hashtags for a longer period of time, and have a better management of your mentions, you should create a new project where you can monitor that specific #hashtag.
Depending on the situation it is recommended that you also monitor the #hashtag keyword without the # sign. For example (#starbucks, starbucks)
BrandMentions allows you to track any hashtag you want. Below is an example for a search on the Starbucks hashtag, for instance.