No app can reliably find a person's social media accounts from a name or phone number, and the manual lookups that actually work are free. Search the exact handle across the platforms you suspect, put the email address or phone number in quotes in Google and Bing, and use the platform's own discovery setting - Instagram and Facebook "find friends" by phone/email, and username search on X and TikTok - because that link is stored by the platform, not by any third-party database.
If the accounts are your own, use Google's "Results about you" to see what surfaces for your name and request removals, and run each platform's account recovery to check which email or number is attached. If you are a parent, Google Family Link lists every installed app on the child's Android phone and lets you block them, and iPhone's Screen Time shows per-app usage - between those two you learn which platforms a child is genuinely using, which is usually the real question behind this one.
If it is another adult, do not build a profile of them. Compiling someone's accounts and activity without consent runs into GDPR's lawful-basis rules in the EU and UK, anti-doxxing and stalking statutes in the US, and platform terms everywhere; paying a "people finder" for social handles mostly buys stale data-broker records resold by whoever bid highest. The lawful routes are their consent, a court order, or a licensed investigator working under one.
Where our product is actually useful: Ultimate Phone Spy shows the installed app inventory on an Android 4.0+ phone you own or administer, with install dates, so you can see which social platforms are present rather than guessing from a username (installed apps). Paired with web history it answers "which sites and platforms is this device really using", and it runs on Windows and Mac too for a family computer. It does not cover iPhone, since iOS blocks device-level access - so for an iPhone the answer stays with Family Sharing, Screen Time and the platform's own privacy settings.