@gymman -- Line doesn't have Discovery feature. So, you'll first need to find the right contact to add, then use Line to message.
In terms of massage guys, here's some tips.
Most gay massages use Line. You can search online for the good gay massage places, then see if they have Line Id or Thailand phone number (+66). Use that to search and add your Line contacts. From there, you can ask for boys photos. After that, you'll know what's next
Alternatively, most of them are also on Twitter. So, you can also search for their Twitter pages which they usually also post Line ID or phone number there. But I find it's more effective to find the Twitter page of the place you like first, then look at similar businesses.
To save you some times, you can try add these Line ID which is a few of my favorite places, if you like hunky men: @jey2spa, @ganymedespa.
Pls also message me if you have some great pointers