Do you guys know any yaoi that uke is being kept like a pet by the seme? Something like ki...

Well…maybe Blood Bank or Royal Servant

http://www.mangago.zone/read-manga/katayoku_no_sokubaku/
http://www.mangago.zone/read-manga/katayoku_no_sokubaku/
Both of these got a uke used as a pet/plaything by the seme.
http://www.mangago.zone/read-manga/sokonashi_freefall_romance/an/sokonashi-freefall-romance-chapter-6.html/3/
This one the Uke was imprisoned by the Seme and the Seme was also a criminal but lol there's hope he'd get out
unlike killing stalking muhaha

There is also this one where the uke is literally a pet but nothing dark like the above ones or killing stalking it's fluffy though if you like the dark ones you wont like it but who knows.
http://www.mangago.zone/read-manga/fortune_fortune/

this one was supposed to be the first but failed Copy paste :
http://www.mangago.zone/read-manga/prisoner_kaen/