While I'm pretty sure you can find a pattern for a peplum tank these days, I've never used one or needed one. You can easily use any natural waist dress pattern and add a short peplum-length skirt instead of the skirt the pattern calls for! And, dress patterns tend to have a better fit than a tank top or blouse pattern, which are usually even looser and hard to fit.
Here's some examples. I've used two methods for converting fave dress patterns to top patterns.
Peplum Top Method 1: Circle Skirt
You don't need a pattern for a circle skirt. There are some great tutorials out there, so check out this or this and cut a 1/2, 3/4, or full circle skirt for your top! The length only needs to be about 8"-10", usually, depending on your height and how long you want the top to be.
Circle skirts are kind of a pain to hem, so for mine I've twice done a lining of self-fabric or coordinating fabric and sew right sides together along the long (outer circle edge) side. Then just sew right sides together on the outer fabric to the bodice, and finish your seam allowance inside.
Circle skirt peplums work well on a fitted top like one of these...
My seersucker princess seam tank and Simplicity 1913
My pleated front bodice from Simplicity 1873
This one actually was a dress first, then a top, made with Simplicity 2444
Peplum Top Method 2: Gathered Skirt
I love the look of the gathered peplum with a double peplum (pepla plural? no...) or with a looser top. Here's some examples...
My recent experimentation with a looser peplum top
And some inspirations for future projects! For these double peplum tops, you'd create two peplum tubes, one shorter than the other, then hem... pin together at the top (raw) edge and gather both as one. Then sew to bodice.
Ready for some springy top-sewing?? Anyone do any great peplum inventions lately?!!