I am sure it would work!
I would like to explain, giving this example:
Crewmembers in our airline have started a Facebook group for switching vacation dates.
In September we usually request the dates we would like to be off work for the complete next year.
There are, of course, certain times nearly everybody would like to have days off, like Christmas or the summer holidays, but of course, this isn’t possible.
In November the company releases the off days for all crewmembers for the next year. We usually are granted at least one of our requests, but not all of them. We cannot simply ask the company for different dates, we need a matching partner to do a switch.
From then on, everybody, who wants to switch dates, posts in this group, something like this: ( …we use # for the month, but I don’t know if this would work here.)
Offer: #January 4-15, 12 days
Search for: #Oktober any, 12 days
Or
Offer: #March 17-31, 15 days can be splitted
Search: minimum of 5 days in either #April, #July, #September or #December
So if I see offers for dates I am looking for, I scan them for my dates. Sounds complicated, but it’s easy.
If there were different threads for the UK, the US, Austalia and mainland Europe, I am sure that this is a great idea.
Of course everybody would need to read through all the posts. It’s work, yes, but it’s also worth it.
I would suggest that all requests should be sent as personal message in order to not confuse everybody else looking for available sitters. As soon as someone finds a match the sitter should delete the post.