Help Please! Found cat!

Hi there! My friends and I have seem to come across a lost cat. One day a very beautiful cat came to our back porch. It looked and acted like a completely domestic cat. It was black and white and the white had not even a smuge. It also had indents around its neck that would sugggest that it once had a colar. Anyway the cat has been in our yard for about a week, we put up lost papers on the lightposts but no one seems to claim the poor cat. We also noticed a hard lump on its back left hind leg that might suggest our friend is sick too. My question is what do you suggest we do? We can not keep the cat because one of my housemates has allergies. But we do not want to send the cat to the shelter where they may put him to sleep because he is sick?

I would post an ad in the local newspaper, take it to any vets to check if he might have a chip, and check some website that post pictures of lost and found pets. Here's two of them :
www.tabbytracker.com
www.petfinder.com
There are lots more, but you can start with these.
I would also take a look at your local craigslist for lost and found.
Good luck !

meowme has some good thoughts there. I'd also research local sanctuaries/rescue groups (Google or Goodsearch to find, or maybe TCS members might have some info if you post requesting SANCTUARY/RESCUE INFO FOR (your location). Contact them, too. They may be able to take him in. ALL THE BEST to him and to you, for caring and trying on his behalf. He sounds like a beautiful cat and he deserves a loving, forever home.

That lump could easily be an abscess--the cat fights, and a fang or claw pierces the skin, and the wound gets infected. If so, it needs vet care... You'll want to do whatever you plan to do pretty soon.

For now, keep him in a single room, so you can keep him away from your allergic roommate...