There are many more than 50 workers that you can recruit so this trophy is quite easy.
There's two ways to recruit: Put out flyers at the Majima Construction menu (talk to Majima once you unlock this minigame), or talking to workers around Sotenbori/Kamurocho once they can be recruited.
To get workers to appear around Sotenbori/Kamurocho you will need to do substories or beat street bosses (these are unlocked by simply fighting lots of random enemies).
Putting out flyers costs money but you can get lots from the Hostess Club minigame, so I'd recommend doing that for a while until you reach 10-15 million, then put out tonnes of flyers.