You remembered where you picked up those small metal nuggets, right? Finding additional ores may require extensive exploration and mining. You should become very familiar with ores and minerals. If you need a specific resource, you must find the rock type it spawns in either under your feet or across the world.
When picking up small nuggets becomes unsatisfying, it is time to start prospecting to find ore veins:
If you're looking for ore veins, and you can't find the vein by guessing, it's time to pull out the prospector's pick. If you are familiar with base prospector's picks in TFC you may be suprised to learn that they function very differently in TerraFirmaGreg
Right-clicking a prospector's pick in TFG will cast a search ray in your views direction. The rays width and depth is dependent on the tier of the pick noted in its tooltips. Depending on the tier of the prospector's pick can also give you a count of the ore quantities and even display an X-Ray indicator of the ore vein.
The prospector's pick can display the following information on use:

Using a prospector's pick looks like this. The large "!" mark particle is from per-vein style x-ray. And the smaller ones are from per-block style x-ray.
To make a prospector's pick, you can knapp an unfired mold out of clay as shown above.
Yellow White****
Once the mold has been knapped, it needs to be fired to create a propick head mold.
To create the tool head, cast liquid metal into the mold.
Tier I
A prospector's pick head can also be smithed out of an ingot of any tool metal on an Anvil.
The prospector's pick is then created by crafting the tool head with a stick.
The majority of the stats and charecteristics of the prospector's picks can be adjustable in your server config file.
Technology is now! And with it comes new ways to find your ore veins!
Ore Prospector's are GregTech's solution to finding ore veins and fluid deposits in your world. The size and capabilities of the ore prospectors are determined by the voltage tier.

An example of what you may see using the LuV ore prospector.