It seems that you have installed polipo or homebrew with root permissions.
Try to set permissions of /usr/local/Cellar/polipo/1.1.1/ according to your username (my username is hamidrohani):
$ ls -lah /usr/local/Cellar/polipo/1.1.1/
total 88
drwxr-xr-x 9 hamidrohani admin 306B Aug 2 02:38 .
drwxr-xr-x 3 hamidrohani admin 102B May 19 02:50 ..
-rw-r--r-- 1 hamidrohani admin 24K May 15 2014 CHANGES
-rw-r--r-- 1 hamidrohani admin 1.0K May 15 2014 COPYING
-rw-r--r-- 1 hamidrohani admin 369B May 19 02:50 INSTALL_RECEIPT.json
-rw-r--r-- 1 hamidrohani admin 622B May 15 2014 README
drwxr-xr-x 3 hamidrohani admin 102B May 19 02:50 bin
-rw-r--r-- 1 hamidrohani admin 816B May 19 02:50 homebrew.mxcl.polipo.plist
drwxr-xr-x 5 hamidrohani admin 170B May 19 02:50 share
or try to reinstall homebrew and then polipo in your current user without any sudo prefixes.
Launch agents will be installed in ~/Library/LaunchAgents. So you can start polipo with Homebrew Services:
brew services start polipo
Homebrew Services will be installed automatically within installation of homebrew; Otherwise install it:
brew tap homebrew/services
After a successful installation, look at here for configurations.