You can't use it to market your Adsense, but you can use it to market your websites. You can do a search for people on Twitter.com and find people who use keywords that you might be after and follow them and hope they follow you back. Otherwise you can download TweetDeck and search for your keywords to see who's talking about things related to your niche. Be aware, you're going to find 90% internet marketers, and hardly any people who would even consider buying products or following internet marketers back. Twitter is quickly turning into a waste of time.