TikTok offers several targeting layers, from broad to deep.
Demographics: location, gender, age, language. This is the base layer every campaign must get right — if it's wrong, nothing downstream can fix it.
Interests and behaviors: target by the content topics users watch (fashion, food, tech…) and interaction behaviors (finished videos in your category, engaged with certain creator types). Useful for splitting messages by segment.
Custom audiences: your own pools — video viewers, page engagers, website visitors (via pixel), or uploaded customer lists. These convert best and power retargeting.
Lookalikes: the system finds people similar to your source pool (usually purchasers). Lookalike quality depends on source quality and size — aim for at least several hundred people.
A common combined strategy: start broad + demographics so the pixel accumulates data, then add custom-audience retargeting, and finally open lookalikes once the purchaser pool is big enough.