I agree.
I am quite shocked by other responses suggesting that covert respect for "preferred pronouns" (by omitting crucial information) should be prioritised over the safety of a missing child.
Runaways are easy prey for predators, which is why predators hang around bus and railway stations offering to "help" lone kids who look lost and in need of somewhere to stay. However, although both girls and boys are trafficked they are more likely to be girls and both boys and girls are more likely to be trafficked by someone they know, including members of their own family, than a stranger.
There are so many ways that a child could experience far worse damage to their mental health than temporary "pronoun annoyance".
However androgynous a photo might be, it is going to be easier in real life to determine whether a teenager is male or female, so this this information is crucial.
Sadly, if they are being trafficked, eg. for sexual exploitation, county lines or modern slavery, then their appearance might be disguised so that they look less like the "Missing Child" photo.
In the UK, "The United Kingdom is the most prominent country of origin for trafficked children – a total of 2,874 reported cases – followed by Vietnam (246 children), Sudan (163 children), Albania (160 children), Romania (138 children) and Eritrea (132 children). Children from Afghanistan, Iraq, Nigeria and Iran also made up significant numbers of those identified."
Home Office, National Referral Mechanism Statistics: UK, End of Year Summary, 2020
https://www.ecpat.org.uk/child-trafficking-statistics
The police are being anything but kind if they collude in disguising or obscuring the sex of a missing child, whether by referring to them as the opposite sex or by omitting to mention their sex.
If the child seeks to present as the opposite sex then it might well be "outing" to state this fact. However, the first responsibility of the police is to protect the child from harm and this information too could be crucial in helping to find the child as soon as possible.
As ever, if Safeguarding is put as the first priority then everything else falls into place and there should be no difficulty deciding not to obscure or misrepresent the sex of a missing child.
IMHO the WDI UK Campaign slogan "End Sex Falsification, Restore Safeguarding, Repeal the GRA" has things in the right order:
https://womensdeclaration.com/documents/451/WDI_UK_Response_to_FWS_v_Scottish_Ministers.pdf
I do believe that the GRA should be repealed but to focus only on the GRA misses the point that sex falsification of any sort always erodes safeguarding and would still need combatting even if the GRA were repealed today.