I just released Transdroid 2.1.3. It includes bug fixes, such as for the rTorrent file upload restriction, but more importantly it supports the new Torrent Search 2.0. With the 2.0 release of the Search module I introduced support for private sites to function just as the public sites that were already supported nicely, fully integrating in the search feature of Transdroid and other apps.
When you open the new Torrent Search interface you can enable and disable public sites in case you are not interested in their content, and Transdroid will not show them in the search results. More importantly, you can provide the credentials to private trackers that you have an existing account for to get the same smooth search experience in Transdroid for your private sites.
Since every private tracker will have a different code and login method, support for each of them has to be custom build. Currently I only support IPTorrents and Bit-HDTV. If you have a private site that you like support for, you may either implement it yourself of course if you know some Java (you can use the IPTorrents class to start) and send me a pull request on GitHub. It is quite simple really. No coding skills (or lazy)? If you provide me with an account I might add it myself — although my time is very limited so I can give no guarantees.