San Diego-based StockTwits, the stock-focused, micro-messaging service run by Howard Lindzon, has launched a new feature today, focused on activity streams. The firm said the new StockTwits Activity Stream will allow users to keep up with other people, as well as tickers friends are following. The stream is very similar to features on Facebook, Google Plus, and other social sites. StockTwits operates a micro-messaging service, similar to Twitter, but focused on discussions and information on stock trading. Lindzon is known for his prior startup Wallstrip, plus his angel investment activity.