Why no mention of the product and a black and white photo?
You're right, it's either an integrated circuit switching regulator IC with transistor(s) in it, or transistor(s) themselves and there's a control IC nearby. So... is there a control IC nearby?
I can't see what the chip on the bottom of the picture is labeled (another reason to do color pics, labels can show up better including if you increase saturation), nor tell where the traces go from here.
Another way to reverse engineer it is to trace where the (presumably buck'd, lower voltage) from that subcircuit goes, and what the power requirements are of what it powers, then look for same size SMD 6 pin chips capable of the voltage and current, at an electronics supply house with a parametric search like Digikey. Get a short list of those chips and then look at the datasheets for their pinouts to see if they match what you see on the PCB.