Hi emilou22,
I would agree with Adam that this does look like a fledgling greenfinch.
At this point, there are a number of considerations you must make to give this bird a chance of survival:
1) First of all, the bird's own parents are those best suited to raise it. If the bird was only picked up today, consider if it can be returned immediately to where it was found to be released in a spot which is safe from cats/other predators/children/traffic. If so, do so, and then keep watch over it from a distance until you are sure that its parents have located it ... may take a couple of hours watching.
2) If point 1) is not practical, then the bird will need a surrogate parent. Best option is to locate a wildlife rescue centre in your area, and phone them.
If they can't help, they may know someone who can. Your local vet may also know of someone with experience of fostering birds, although don't expect the vet to take the bird in.
A list of some rescue centres is available on this website at this address:
Wild About Britain
Don't hang about though, as the bird will need to be fed soon.
3) If you can't find someone in your area to help you, you will need to assume the parenting role yourself ... this is time consuming, and requires both dedication and stamina, but provided that the bird is uninjured by the cat, it can be done successfully following instructions that we can give to you.
Let us know what you plan to do, so we can provide further support as necessary?