KMB/Citybus number 171 goes from Lai Chi Kok to South Horizons (SH is on Ap Lei Chau and about a 10 minute walk from Horizon Plaza).
This bus route is high frequency (every 4-9 minutes throughout the whole day). It goes from LCK down Cheung Sha Wan Rd, Nathan Rd (to Yau Ma Tei), then to Hung Hom, then through cross harbour tunnel, then through Aberdeen Tunnel, then a short way to Ap Lei Chai. Cost is $11.10.
From Tsing Yi to Lai Chi Kok should be a short Taxi ride. Or you can take MTR to Lai Chi Kok.