Now what!
 

Max our new yorkie was at my birthday party (still can't be left... Cries non stop) He was running on wood tiles we were laying out on the floor. He yelped then wouldn't put weight on that leg... I had the vet check him for luxating patella on his wellness check at 8 weeks but they said pups that young have unstable knees until they are older. Don't tell me this little guy has a heart murmur and luxating patellas. Is there anything else to watch on his knees? I don't let him go on stairs or put him on furniture. He sleeps wedged between my husband and my pillow with his kennel between us too so he can't jump down off the bed. Plus we have the shortest bed available because one of our shiz tzu's has legs about 5" long and can't jump up.
Running around again and putting weight on that leg now so what do you do now for this? Vet check or just try to keep him quiet?

He could've just pulled / strained something a bit - so I'd give it a day or 2 to see if it just resolves.

When one of my dogs limp, I gently run my fingers down his leg, you can pull gently back on his leg, be sure you feel his pads for a stone or sticker, also just at the top of his leg for same. I hope he is ok :)
:)

There isn't much you can "do" except to have the knees examined when he goes to the vet as he grows. Luxating Patella is hereditary and if they have it , only will get worse with time. They will " grade " it as time goes on.in the meantime pay close attention as he grows as to how he carrys himself and watch those hind legs for skipping, bunny hopping, and leg carrying , as these are certain signs of a progressive problem that you will have to get serious about.this is what I am going thru right now with 3 yr old Zoey. She was diagnosed at about a yer old ....it didn't start getting bad till an abrupt wind shoved the side door on her and popped her out on the other side scraping her leg ....
She only favored it for 2 days then was running like nothing happened. We just noticed the "popping" of her kneecaps a LOT so we had to pursue it. 4 vet opinions later we just had double knee surgery and brought her home yesterday.
They said both knees were equally bad although she sat on the round of her butt on left side only with right leg extended....and the cartilage was starting to wear.
So yeh take note on how they sit and sit up which she got so she couldn't do...and you'll know something is wrong if it gets worse.
Good luck...hop this helps.