Daniel Glazer, partner at Fried Frank has done a good article on how European companies seeking US venture capital should go about it. 

In our experience the chances of a European company raising a decent seed, angel or series A round in the US are very low, unless the company is prepared to move lock stock and barrel to the US. Most US VCs require the CEO/founder to be already living in the US with great customer traction in North America, to even look at the pitch. 

Once you get to the growth stage, however, with significant revenues, the picture changes. For companies looking for capital to accelerate an existing international business, we see increasingly high levels of interest and activity from a growing number of US funds. These tend to be the sorts of situations where a growth stage adviser like FirstCapital, with our network and experience, can really help.