For every plated bullet I shoot (Berry's), I use the starting load data for a copper jacketed bullet and work up from there.
For peace of mind, compare the max loads for lead bullets and minimum loads for FMJ/jacketed bullets of the same weight. That will give you a good idea where to start. Many plated bullet manufacturers have maximum velocity data on their websites too.
38 Caliber 158 grain Lead Round Nose/Bullseye. Max 3.6 gr.
38 Caliber 158 grain Jacketed Hollow Point/Bullseye. Min 3.3 gr. Max 4.1 gr.
(Hornady Handbook, Third Edition).
Based on this information, I would step ladder load some .38 Special Plated bullet loads with 3.3 grain and 3.6 grain. If all works out well, and you see no signs of excessive pressure, you can go up some more until you find the "sweet" spot, but never exceed max!
The most accurate load for your firearms will almost always be far lower than the safe maximum pressure.
Always consult a reputable reloading manual and don't trust anything someone tells you on a forum.
Use the lead (non-jacketed) data. It probably won't mean much on the .38, but at .357 velocities you can have problems. Plated bullets don't have as thick of a layer of copper as jacketed bullets; that's why they behave more like lead.
I've used plated bullets and found them to work just fine - as long as you don't push the velocity too hot.