I've never used Twitter, but when I owned a couple of rare last names I used Facebook and LinkedIn (best option as they are generally professionals and want their last name) and made a couple decent sales off drops ($17 turns into $500-$700).
I don't know exactly what you're trying to sell, but I find cold calling the best as you can directly relate to them. Get to know them, about their business, then talk about a better fitting domain and how it can help themâthen the closer (which people find the hardest, at least I did), ask for the money. They will generally be hesitant and say no, but say that it is safe using an Escrow service to ease their mind.
Ask them something along the lines of, "In your opinion, do you feel that this domain would best suit your company at a later date when you expand?", if the answer is "Yes" you can try a hard close at a discount, if the answer is "No", ask "Would you like me to check back with you after you research the potential of owning this domain and how it can benefit you in future business?". If the answer is "Yes", mark it as a lead, give it a couple weeks and call back. If the answer is no, leave them alone.
Finding end users isn't that tough, it's one Google search away.
Good luck!