479785 Twitter Automated Direct Messager

Hi, I am looking for a web based application or website what does the following: 1, connect to twitter 2, find people who has tweeted a specific keyword (loose weight, stop smoking) 3, tweet directly to them (using (at)) a pre defined message 4, can do it automatically! (I can set time frame, number of posts, messages, etc) please, only apply if you are experienced, if you have similar developed already that is a BIG bonus!