Besides the hashtag search, here are two great web services you can use to keep track of the trending topics online.
This is my number one platform when looking for the hottest topics people are searching for online. Google Trends works by analyzing a portion of Google searches to compute how many searches have been done for the terms entered, relative to the total number of searches done on Google over the same time.
Similar to Google Trends, YouTube Trends provides users with stats about the most popular videos in a particular region. Users filter their searches using criteria such as demographics, , age, gender. Trendsmap is another great service included within YouTube Trends and which provides mapped stats about the trending videos in different states.