Try playing a youtube video or a recording of a lovebird chirping and making noise, see if that gets his attention! You can also try putting a cage with a little food outside too
They said that it might land on your shoulder, so I'm guessing that it's tameOh poor little thing.
The owners must be very upset, I know what it's like to lose a pet. Not knowing might be the worst part.
Hopefully it's tame.
Play lovebird noises and call out to it.
When it gets hungry and cold it may come down for food.
I wish someone as thoughtful as you would put in the time to help me find my little budgie
Good luck.