Well that sort of obsessive thinking is something that I think present day culture seeks to instill in people, if you consider the confluence of government and other agencies trying to stoke peoples social conscience or conscentiousness per se or personal responsibility on one hand (because there really are people who need to get that message) or the message of "you really need to get one of these" of maximal consumerism, which isnt just the invention of marketing or PR men but is carried on like a "mind virus" by people themselves, especially brand conscious cliches or niche identities.
During the cold war paranoia was a big, big deal and if you werent actually thinking that way you could be deemed to be unaware or unpatriotic or something.
You just need to repeatedly ask yourself is what you're thinking rational? And consciously correct your own thinking, because something is possible doesnt mean its probable, so just because its possible that your friend being out of contact could mean they are dead definitely does not mean its probable, unless they are a soldier or living with high risk.
I have thoughts like that now and again, particularly when I'm stressed, often when I'm in contexts were the probabilities are high there's going to be stress accompanying that, but I just keep catching myself thinking that way and then consciously question it, on the basis of what evidence am I thinking that. Could be irrational, no evidence.
If it is true/there is evidence is it something I can influence, could I? Should I? So even if its probable, maybe its something I shouldnt worry about or cant influence anyway. The worry is meant to be a signal to action but if no action is possible, or you've taken what action you can, then just dispensing with the worry is the logical thing because its not serving any good purpose.
Even when there's evidence and its not a straight forward irrational assumption or jumping to improbable conclusions there's explanatory style to consider, my explanatory style is pretty optimistic (people arent going to believe that because a lot of my posts are decrying the ludicrous misdirection I think the world is taking most of the time), so in the given example I would think no news is good news, bad news travels fast, therefore if I havent heard anything from anyone I wouldnt assume the worst (they could have won the lottery and are off spending their fortune and good luck to them).
You might need help, then again maybe not, like I say I think that there's a great deal of this sort of ordinary misery created by our pop culture, or it underpins social structures or social stratification, everyone experiences it in varying degrees but some people are just fortunate that it doesnt trouble them so much or they have a great informal network of support.