I'm a speaker of Klingon and co-founder of the former Klingon Wikipedia, which got moved to Wikia. There are no native speakers of Klingon. There used to be one, the son of D'Armond Spears, but he ceased to speak the language when he was about 4 years old. It's a well-known story. So unless there's a fluent speaker who manages to keep it completely secret that they're speaking Klingon with their child, unbeknownst to the speakers' community, then there is no other native speaker of Klingon at the moment.
With about 20 to 30 fluent speakers and maybe around 200 (my guess) who can communicate in the language well enough, it is at least a possibility.

- André

2017-12-09 17:46 GMT+01:00 Milos Rancic <millosh@gmail.com>:
This [1] sounds like pretty valid and "maybe few" is infinitely larger
number than 0. Besides the fact that you told me the same information
~5 years ago.

The insult was intentional.

[1] http://blog.longnow.org/02009/06/01/klingon-elvish-and-esperanto-linguist-takes-a-serious-look-at-invented-languages/

On Sat, Dec 9, 2017 at 5:36 PM, Gerard Meijssen
<gerard.meijssen@gmail.com> wrote:
> Hoi,'
> and you have it on good authority that there are native speakers of Klingon?
> Who are you fooling. At that, you are insulting.
> Thanks,
>      GerardM
>
> On 9 December 2017 at 17:10, Milos Rancic <millosh@gmail.com> wrote:
>>
>> I suppose you have strong evidence that LFN has more native speakers
>> than Klingon or you are just an ordinary liar?
>>
>> On Sat, Dec 9, 2017 at 4:45 PM, Gerard Meijssen
>> <gerard.meijssen@gmail.com> wrote:
>> > Hoi,
>> > In an alternate universe maybe.
>> > Thanks,
>> >      GerardM
>> >
>> > Op za 9 dec. 2017 om 13:24 schreef Milos Rancic <millosh@gmail.com>
>> >>
>> >> I've just said that Klingon makes more sense than LFN, as it actually
>> >> has
>> >> native speakers.
>> >>
>> >>
>> >> On Dec 9, 2017 06:55, "Gerard Meijssen" <gerard.meijssen@gmail.com>
>> >> wrote:
>> >>>
>> >>> Hoi,
>> >>> We had Klingon at one time.. Do you really consider revisiting that ?
>> >>> Thanks,
>> >>>      GerardM
>> >>>
>> >>> On 8 December 2017 at 23:22, Milos Rancic <millosh@gmail.com> wrote:
>> >>>>
>> >>>> On Fri, Dec 8, 2017 at 10:58 PM, MF-Warburg
>> >>>> <mfwarburg@googlemail.com>
>> >>>> wrote:
>> >>>> > Can we, by the way, define more detailed criteria for which
>> >>>> > artificial
>> >>>> > languages should be eligible?
>> >>>>
>> >>>> Agreed. If we count native speakers, Klingon is, AFAIK, immediately
>> >>>> after Esperanto.
>> >>>>
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>> >>>
>> >>>
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