Altmetrics, or “alternative metrics,” refers to an emerging field of new methods for measuring the use and importance of scholarly articles, particularly in the sciences. As opposed to more traditional bibliometrics, such as Impact Factor, altmetrics provide article-level data and are based on new electronic sources of information, such as number of downloads and page views from a publisher, repository or online reference manager like Mendeley, or the amount of discussion generated in online venues such as Twitter or blogs.
Because altmetrics is a fairly new idea, there aren't many sources available for tracking them. Many sources ask their customers to pay for a subscription, either at an individual or organizational level.
One of the best resources to use is ImpactStory. ImpactStory uses a variety of metrics to measure the impact of articles, slides, and software. You will need to create an account to get started.
Impact story will provide you with data about the number of shares, views, bookmarks, or tweets each item had. Hover over an item to get an explanation of why it was ranked.
Another service, entitled Altmetric, offers similar information. The data that Altmetric provides, however, is much more advanced. It provides an Altmetric Attention Score, which serves as an indicator of the overall volume and nature of attention that research has received online. Altmetric also provides a bookmarklet and app that make altmetrics more mobile and convenient. Please note that Altmetric costs money to subscribe to and is based out of the UK.