I'm sorry it didn't work. See if any of my suggestions below give you some ideas for trying again (maybe not...but I can always hope

).
The style of asking may make a difference, depending on the list you (this is now a generic "you" = anyone reading this message) post an announcement on.
Which of the following (hypothetical) WANTED requests might evoke the desired result? That is, people emailing you with an offer to come pick up some planting pots.
1) WANTED: Small Planting Pots [name of town]
==>I'd like to get a head start on my spring garden, and start veggie seeds in small planting pots. If you have unused, unloved plastic, paper, peat (or even clay!) planting pots, especially small ones, I will give them a mission in life and an appreciative home.
Thank you!
or (and I see this a lot..)
2) WANTED: Pots
==>I'm looking for pots for seeds so I can start my veggies for spring. If you have extras, please let me know; I can come and get them.
Thank you.
I have no idea whether you wrote an announcement like #1 or like #2 (this post is more of a "general FreeCycle insider view" compendium of advice), but #2 makes the reader do a LOT of work:
First, s/he needs to figure out what kind of "Pots": kitchen pots? garden pots? oh, probably garden pots. OK...plastic? clay? cardboard? peat? (and the reader hasn't even gotten past the "WANTED" line yet)
Second, what town/neighborhood are you in? In many places, this makes a difference; people like to feel that they're helping a "neighbor" or "someone I could know." Weird, but there it is.
Third, and now we're finally reading the text..."pots for seeds" Aha!
That's what he wants! "Start my veggies"--for non-gardeners, even people who live with a gardener, starting seeds when there's snow on the ground seems, um, odd. So those non-gardening partners and all those non-gardening households who have someone else's stuff in the garage/on the porch won't make the connection between their pots and your seeds.
The word "extras" seems to be an unspoken taboo on FreeCycle. One of the lists I belong to is probably the most unconventional in our country (it even allows cross-talk and conversational threads), and the other two are pretty vanilla: Wanted, Offered, Taken, Received, and the occasional Thank You, FreeCycle! But no one on any of these lists, nor on a fourth to which I belonged for two years, has ever used the word
extra that I can remember. "I can come and get them" isn't special; it's expected.
True-life example: When someone asked for a crockpot and DH and I had just retrieved one from the depths of his mother's garage, never used, in original packaging from the mid-'70s, I was careful to refer to it as "that" crockpot. Then, one wonderful day not a month later, a "WANTED: Crockpot" post showed up. I had already given away my old 2-quart crockpot in an upgrade to a 4-quart, but now I had "that" crockpot. The requester said that, due to the cold weather, she had realized that she really needed to set up dinner before she left for work in the morning and that it would make a real difference to her state of mind coming home if she knew that a warm meal was waiting for her because of a crockpot.
A match made in heaven. But I didn't have an
extra crockpot; I had
hers!
Somebody is bound to have
your planting pots; try another list, if there is one, or try a different announcement. Some lists have rules about not asking more often than once a week--each list is free, within limits, to set its own policies--so check with the moderator to make sure you're not doing anything against that particular list's rules.
The one absolute, ironclad rule for FreeCycle is: No money changes hands. Nowhere, nohow, notime, noway.
Cynthia