So on my current playthrough i found a stray dog and ist no longer around,I tryed buying a dog in markarth but is says I allready have one with me but I dont see him anywhere.
Any help ?

He's either:

A) Stuck somewhere... try fast travelling to see if he arrives with you.
B ) Been told to wait somewhere... after three days he should go back home. Try waiting that and see if you get a message about it.
C) Chasing butterflies...
D) Invisible! OooOOOoOOOOOoooooo

Probably one of the first two though.

thank you ill try.

Was it a stray dog or was it meeko. If it was a stray dog you might be out of luck. They leave you at some point and if it's saying that you might not be able to do anything about it. If it was meeko just go back to meekos shack, he should be near the road.