I have a horrible theory (since I’d like to think Rumple’s changed a bit, but he did have Smee locked up somewhere for at least a little while…) that Gold’s got August hidden away somewhere. Why? August is a threat: He knows about the dagger, and actually tried to use it to control Gold. Gold has good reasons to not want lots of people knowing about that dagger, especially with magic back.
Alternatively, Gold’s been a little distracted since magic came back with his Bae quest and Belle’s presence. Maybe he didn’t take the precaution of securing August. August knows full well that Gold’s aware now of what he knows and only let him go because he wanted the curse ended. If he’s got any sense, he went into hiding outside of Storybrooke–assuming that magic allowed him the ability to do so. He was never cursed, so he could leave without losing his memories.
It’s possible he has other motives for hiding out–shame or fear with regards to his father/Blue. Or some temptation out there. But at this point I strongly suspect that either Gold knows exactly where he is, or August is doing everything in his power to prevent that.
Keeper of Belle's Gold magic, sand dollar, cloaks, purple FTL outfit, spell scroll, library key, copy of Romeo and Juliet, and cry-muffling pillow, Rumple's doll, overcoat, and strength, and The Timeline. My spreadsheet: https://drive.google.com/file/d/0B6r8CySCCWd9R0RUNm4xR3RhMEU/view?usp=sharing