To get the VM status from all your virtual servers:
https://$user:$apiKey@api.softlayer.com/rest/v3/SoftLayer_Account/getVirtualGuests?objectMask=mask[powerState]
Method: Get
Note: Replace $user and $apiKey with your own information
To get the VM status from a list:
https://$user:$apiKey@api.softlayer.com/rest/v3/SoftLayer_Account/getVirtualGuests?objectMask=mask[powerState]&objectFilter={"virtualGuests":{"id":{"operation":"in","options":[{"name":"data","value":[$vsiId1, $vsiId2, $vsiId3]}]}}}
Method: Get
Note: Replace $user, $apiKey, $vsiId1, $vsiId2, $vsiId3 with your own information, you can add more ids, separating by ","
Updated
cURL
If you are using curl, you should send the command encoded, because we are using filters in the request, so it should look like this:
curl "https://$user:$apiKey@api.softlayer.com/rest/v3/SoftLayer_Account/getVirtualGuests?objectMask=mask%5BpowerState%5D&objectFilter=%7B%22virtualGuests%22%3A%7B%22id%22%3A%7B%22operation%22%3A%22in%22%2C%22options%22%3A%5B%7B%22name%22%3A%22data%22%2C%22value%22%3A%5B25129322%2C15535999%5D%7D%5D%7D%7D%7D"
Replace: $user, $apiKey, 25129322 and 15535999 with you own information
The VSI identifiers that I'm looking for are: 25129322 and 15535999, as you can see, they are encoded in the command