As with all Catholic saints, it is always appropriate to make a small donattion to a Catholic charity, or to any charity that helps in cases similar to what you petitioned for. In other words, you wanted contact from a "missing" person, so a small donation to a missing persons fund in the name of Saint Martha would be acceptable. To give another example, if you had petitioned Saint Francis for the health of a pet bird, a donation to a bird sanctuary in the name of Saint Francis would be acceptable.
There are two spirits called Saint Martha: They are
1) Saint Martha the Dominator of Bethany [Judea] and Tarascon [France], a contemporary and friend of Jesus Christ and a saint of the Catholic church, and
2) Filomena Lubana, an African woman / spirit whose nickname is Saint Martha the Dominator, although she is NOT a Catholic saint and probably was never a Christian.
Here are their statues, which we sell in our shop:
STA-CAS-MA12
12" St. Martha Dominator w/ Dragon Hand-Painted Resin Statue
$47.00

You can order right here in the Forum by clicking on the blue Add To Cart button.
STA-CAS-MD13
13" St. Martha Dominator Lubana Statue w/ Snake Hand-Painted Resin Statue
$36.00

You can order right here in the Forum by clicking on the blue Add To Cart button.