Tesla's European sales tanked in August.

Tesla ( TSLA -4.38% ) stock has been on a big run, but it lost some steam today. Shares of the electric vehicle (EV) maker slid as much as 5.4% in Thursday trading. The stock closed the session lower by 4.3%.

While the company has been focusing more of its message toward artificial intelligence (AI) and robotics opportunities, investors seem to still be concerned about slowing EV sales.

Tesla keeps losing ground

New EV sales data show Tesla continues to lose its lead versus EV competition. August sales data from the European Automobile Manufacturers' Association (ACEA) showed Tesla sales dropped 37% year over year in the European Union.

At the same time, August was a banner month for Chinese competitor BYD . Its August sales tripled ye

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