I don't know about you, but that sounds unnatural to me. "I am in" would be perfectly fine - maybe not something I would say in my dialect, but OK nonetheless - but "I am in, playing" feels like you're artificially making the sentence shorter by sacrificing actual meaning.
Dutch doesn't have exact continuous form, so present form can be used for continuous form. However Dutch use emphasis to say that the person is doing something; one of the ways is using "aan het." "Aan het" is basically "on something". Like for example, "hij is aan het lezen" means "he is on the reading" or something like that.