There are no actual statistics kept on this, but if you put 'actors died drug overdose recent' or similar terms in a search engine, you will find various answers. These aren't official though, and mostly look at such deaths over a period of many years rather than the last few.
In fact actors in general aren't necessarily more likely to die in this way than the general population. Partly, it's because of media coverage that we notice it more when a star dies of an overdose, and probably with the 'Hollywood lifestyle' there is more exposure and more temptation etc, so you may get more drug use - but most actors of course don't really live that lifestyle anyway.
Recent sad deaths like that of Philip Seymour Hoffman have prompted a lot of people to create lists of similar celebrity deaths - you can find one example here.