TwitterMass is an excellent site for those planning to build a formidable network of twitter followers.

The site helps you find twitter users based on keywords. You then have the option to mass follow all such users just like you can with other similar twitter apps like Twollow and TwitterPerch. You can also @reply personalized messages to all the newly followed users.

The site also provides an excellent #FollowFriday feature. Just select the Auto Follow Friday option and every friday a set of your twitter followers would be tagged with the #FollowFriday hashtag automatically. The site takes the number of RT, @replies and other mentions of your username into account before suggesting a followfriday on your behalf.

If at any point of time you do not wish to continue with your twittermass account you can easily delete the account as well.