is a dating website with a free option. There is no field for a poly person, but there is a field for sexual orientation you can search on. Some people have "polyamory" in their profile, some do not. But I have heard there are a few poly people on there.
is a social website, but they have forums (called "groups") for dating ads. Some are not specific to a region, some groups are specific to a region. Look for your state, province or country along with the word "polyamory". Example: Kansas polyamory.
Please note: not all groups are appropriate for placing ads. Read the group header first for rules.