this is simple... BUY A NEW ONE. they are cheap and even though oiling a rusty chain can get it to move again, one link or plate that got too weak may snap the whole thing. i got an cruiser from a friend of mine who had it in his back yard. he decided to get on it, mash on the pedels just long enough for the chain to SNAP send him terra firma fastly. a week later, i bought it, repaired the same chain and oiled it (it was rusty but not uber rusted), got on it and after about 3 miles of riding, SNAP! luckily it only sent me flying to the ground where my face broke my fall.
new chain.