I think your little dog looks a bit like a Jack-chi. I have one and yours looks like it may be a long haired chihuahua and Jack Russell mix. Also, the ears look like they may be chihuahua too. His face looks like a Jack Russell and the markings. They are breeding Jack-Chi's now quite a bit so this may be one.
I have two jack Russell both are different breeds and this dog certainly has some features that do look like that of a jack Russel. However I feel that he is too fluffy to be a jack Russel, also his ears are fairly big whereas jack Russell ears tend to be much smaller.I think he may be a jack Russel cross; have you tried getting a vet to have a look at him they are usually pretty accurate in telling breeds and even cross breeds. A really cute dog though, hope this helped.